diff --git a/docs/Reference/config/config_schema.json b/docs/Reference/config/config_schema.json
index 696ff76b1..a112b09ec 100644
--- a/docs/Reference/config/config_schema.json
+++ b/docs/Reference/config/config_schema.json
@@ -2838,7 +2838,7 @@
           "value": 1.0
         }
       ],
-      "description": "Cryoscopic depression factor controlling the width of the mushy zone (partially molten region) in the PALEOS unified EOS. Defines the solidus as T_sol = T_liq * mushy_zone_factor. 1.0 = sharp phase boundary (no mushy zone). 0.8 = solidus at 80% of the liquidus temperature, roughly matching the Stixrude+2014 cryoscopic depression for MgSiO3. Must be in [0.7, 1.0]. Only applies to PALEOS unified EOS; ignored for WolfBower2018 and RTPress100TPa (which use explicit melting curve files). This factor is applied consistently across Zalmoxis (density interpolation), SPIDER (phase boundaries), and the VolatileProfile phi-blending.",
+      "description": "Cryoscopic depression factor controlling the width of the mushy zone (partially molten region) in the PALEOS EOS family. Defines the solidus as T_sol = T_liq * mushy_zone_factor. 1.0 = sharp phase boundary (no mushy zone). 0.8 = solidus at 80% of the liquidus temperature, roughly matching the Stixrude+2014 cryoscopic depression for MgSiO3. Must be in [0.7, 1.0]. Applies to the PALEOS EOS family (PALEOS, PALEOS-2phase, PALEOS-API, PALEOS-API-2phase); ignored for WolfBower2018 and RTPress100TPa (which use explicit melting curve files) and for Seager2007/Analytic (no derived solidus).",
       "doc_source": "attributes",
       "group_order": 0,
       "group_position": 3,
diff --git a/docs/Reference/config/interior.md b/docs/Reference/config/interior.md
index 5e14b4fc3..cf364f4a0 100644
--- a/docs/Reference/config/interior.md
+++ b/docs/Reference/config/interior.md
@@ -49,7 +49,7 @@ belong to the experimental binodal-aware mode.
 | `core_eos` | str | `"PALEOS:iron"` | EOS for the core layer. Format: "<source>:<material>". Tabulated: "PALEOS:iron" (default), "Seager2007:iron". Analytic: "Analytic:iron", "Analytic:MgFeSiO3", etc. |
 | `mantle_eos` | str | `"PALEOS:MgSiO3"` | EOS for the mantle layer. Format: "<source>:<material>". Tabulated: "PALEOS:MgSiO3" (default), "PALEOS-2phase:MgSiO3", "Seager2007:MgSiO3", "WolfBower2018:MgSiO3". Analytic: "Analytic:MgSiO3", "Analytic:MgFeSiO3", etc. |
 | `ice_layer_eos` | str or none | `none` | EOS for the ice/water layer (3-layer model). 'none' for 2-layer model (core + mantle only). Tabulated: "PALEOS:H2O", "Seager2007:H2O". Analytic: "Analytic:H2O". |
-| `mushy_zone_factor` | float | `0.8` | Cryoscopic depression factor controlling the width of the mushy zone (partially molten region) in the PALEOS unified EOS. Defines the solidus as T_sol = T_liq * mushy_zone_factor. 1.0 = sharp phase boundary (no mushy zone). 0.8 = solidus at 80% of the liquidus temperature, roughly matching the Stixrude+2014 cryoscopic depression for MgSiO3. Must be in \[0.7, 1.0\]. Only applies to PALEOS unified EOS; ignored for WolfBower2018 and RTPress100TPa (which use explicit melting curve files). This factor is applied consistently across Zalmoxis (density interpolation), SPIDER (phase boundaries), and the VolatileProfile phi-blending. Must be >= 0.7 and <= 1.0. |
+| `mushy_zone_factor` | float | `0.8` | Cryoscopic depression factor controlling the width of the mushy zone (partially molten region) in the PALEOS EOS family. Defines the solidus as T_sol = T_liq * mushy_zone_factor. 1.0 = sharp phase boundary (no mushy zone). 0.8 = solidus at 80% of the liquidus temperature, roughly matching the Stixrude+2014 cryoscopic depression for MgSiO3. Must be in \[0.7, 1.0\]. Applies to the PALEOS EOS family (PALEOS, PALEOS-2phase, PALEOS-API, PALEOS-API-2phase); ignored for WolfBower2018 and RTPress100TPa (which use explicit melting curve files) and for Seager2007/Analytic (no derived solidus). Must be >= 0.7 and <= 1.0. |
 | `mantle_mass_fraction` | float | `0` | Fraction of the planet's interior mass corresponding to the mantle. Required for 3-layer models (with ice layer) and for T-dependent 2-layer models (WolfBower2018, RTPress100TPa) where it partitions mass between core and mantle layers. Must be >= 0 and < 1. |
 | `dry_mantle` | bool | `true` | Structure EOS assumes a dry mantle. Set False for melt-fraction-aware dissolved-volatile mixing in the mantle density (per-shell volatile profile); the dissolved mass then stays inside the interior mass target. |
 
diff --git a/src/proteus/config/_struct.py b/src/proteus/config/_struct.py
index 7a0bfe455..fc0a5a14a 100644
--- a/src/proteus/config/_struct.py
+++ b/src/proteus/config/_struct.py
@@ -50,12 +50,13 @@ def valid_zalmoxis(instance, attribute, value):
     import logging as _logging
 
     _log = _logging.getLogger('fwl.' + __name__)
-    # mushy_zone_factor only applies to PALEOS unified tables
+    # mushy_zone_factor scales the derived solidus only for the PALEOS EOS family
+    _MZF_EOS_PREFIXES = ('PALEOS:', 'PALEOS-2phase:', 'PALEOS-API:', 'PALEOS-API-2phase:')
     mzf = getattr(instance.zalmoxis, 'mushy_zone_factor', 0.8)
-    if mzf < 1.0 and not mantle_eos.startswith('PALEOS:'):
+    if mzf < 1.0 and not mantle_eos.startswith(_MZF_EOS_PREFIXES):
         _log.warning(
             'mushy_zone_factor=%.2f has no effect with mantle EOS %s. '
-            'The mushy zone factor only applies to PALEOS unified tables. '
+            'The mushy zone factor applies only to the PALEOS EOS family. '
             'For WolfBower2018/RTPress100TPa, the mushy zone is defined by '
             'the solidus/liquidus melting curve files.',
             mzf,
@@ -102,16 +103,15 @@ class Zalmoxis:
         Tabulated: "PALEOS:H2O", "Seager2007:H2O". Analytic: "Analytic:H2O".
     mushy_zone_factor: float
         Cryoscopic depression factor controlling the width of the mushy
-        zone (partially molten region) in the PALEOS unified EOS.
+        zone (partially molten region) in the PALEOS EOS family.
         Defines the solidus as T_sol = T_liq * mushy_zone_factor.
         1.0 = sharp phase boundary (no mushy zone).
         0.8 = solidus at 80% of the liquidus temperature, roughly
         matching the Stixrude+2014 cryoscopic depression for MgSiO3.
-        Must be in [0.7, 1.0]. Only applies to PALEOS unified EOS;
-        ignored for WolfBower2018 and RTPress100TPa (which use explicit
-        melting curve files). This factor is applied consistently across
-        Zalmoxis (density interpolation), SPIDER (phase boundaries),
-        and the VolatileProfile phi-blending.
+        Must be in [0.7, 1.0]. Applies to the PALEOS EOS family (PALEOS,
+        PALEOS-2phase, PALEOS-API, PALEOS-API-2phase); ignored for
+        WolfBower2018 and RTPress100TPa (which use explicit melting curve
+        files) and for Seager2007/Analytic (no derived solidus).
     mantle_mass_fraction: float
         Fraction of the planet's interior mass corresponding to the mantle.
         Required for 3-layer models (with ice layer) and for T-dependent
diff --git a/tests/config/test_struct.py b/tests/config/test_struct.py
index 69e714c03..a8bd30de7 100644
--- a/tests/config/test_struct.py
+++ b/tests/config/test_struct.py
@@ -13,6 +13,8 @@
 
 from __future__ import annotations
 
+import logging
+
 import pytest
 
 from proteus.config._struct import Struct, Zalmoxis
@@ -160,3 +162,52 @@ def test_spider_module_skips_the_gate(self):
         # absent.
         with pytest.raises(ValueError, match='core_eos'):
             Struct(module='zalmoxis', zalmoxis=Zalmoxis(core_eos='no_colon'))
+
+
+class TestZalmoxisMushyZoneWarning:
+    """The mushy_zone_factor no-effect warning must fire only for the EOS
+    families that actually ignore the factor.
+
+    mushy_zone_factor scales the derived solidus ``T_sol = T_liq * mzf`` for
+    the PALEOS family (unified, 2-phase, and the API variants) through
+    ``load_zalmoxis_solidus_liquidus_functions``. For WolfBower2018 and
+    RTPress100TPa the melting curves come from file and the factor is inert,
+    so there the warning is correct and must still fire.
+    """
+
+    @staticmethod
+    def _warns(caplog, mantle_eos, mzf=0.8):
+        """Construct a zalmoxis Struct and report whether the no-effect
+        warning fired for ``mantle_eos`` at the given factor."""
+        caplog.clear()
+        with caplog.at_level(logging.WARNING, logger='fwl.proteus.config._struct'):
+            Struct(
+                module='zalmoxis',
+                zalmoxis=Zalmoxis(mantle_eos=mantle_eos, mushy_zone_factor=mzf),
+            )
+        return any('has no effect' in r.getMessage() for r in caplog.records)
+
+    def test_warning_silent_for_the_paleos_family(self, caplog):
+        """Each PALEOS-family EOS feeds the factor into the derived solidus, so
+        the no-effect warning must stay silent for all four."""
+        for eos in (
+            'PALEOS:MgSiO3',
+            'PALEOS-2phase:MgSiO3',
+            'PALEOS-API:MgSiO3',
+            'PALEOS-API-2phase:MgSiO3',
+        ):
+            assert not self._warns(caplog, eos), eos
+
+    def test_warning_fires_for_file_curve_eos(self, caplog):
+        """WolfBower2018 and RTPress100TPa read melting curves from file, so the
+        factor has no effect and the warning must fire."""
+        for eos in ('WolfBower2018:MgSiO3', 'RTPress100TPa:MgSiO3'):
+            assert self._warns(caplog, eos), eos
+
+    def test_warning_tracks_the_factor_not_only_the_eos(self, caplog):
+        """The warning depends on mushy_zone_factor < 1: at the sharp-boundary
+        value 1.0 an ignored setting is not misreported."""
+        assert not self._warns(caplog, 'WolfBower2018:MgSiO3', mzf=1.0)
+        # Paired positive: the same EOS at 0.8 fires, so silence at 1.0 is the
+        # factor guard rather than the EOS being exempt.
+        assert self._warns(caplog, 'WolfBower2018:MgSiO3', mzf=0.8)