diff --git a/consensus/fast_confirmation/benches/fcr_bench.rs b/consensus/fast_confirmation/benches/fcr_bench.rs
index dbe109b4596..ae8f7a816ab 100644
--- a/consensus/fast_confirmation/benches/fcr_bench.rs
+++ b/consensus/fast_confirmation/benches/fcr_bench.rs
@@ -85,7 +85,7 @@ const SCENARIOS: &[Scenario] = &[
 fn block_root_at(slot: u64) -> Hash256 {
     let mut preimage = [0u8; 16];
     preimage[..8].copy_from_slice(b"fcr-root");
-    preimage[8..].copy_from_slice(&(slot + 1).to_le_bytes());
+    preimage[8..].copy_from_slice(&slot.to_le_bytes());
     Hash256::from_slice(&hash_fixed(&preimage))
 }
 
diff --git a/consensus/fast_confirmation/src/lib.rs b/consensus/fast_confirmation/src/lib.rs
index b4fed7304cd..c805a90f4d5 100644
--- a/consensus/fast_confirmation/src/lib.rs
+++ b/consensus/fast_confirmation/src/lib.rs
@@ -18,8 +18,9 @@
 //! 2. **Cached spec helpers**: `is_one_confirmed` still reads as
 //!    `support > compute_safety_threshold`, but `get_attestation_score` is backed by a
 //!    precomputed chain score cache. The FFG predicates compute `compute_honest_ffg_support`
-//!    internally; their call sites are short-circuited, so the O(V) FFG sweep only runs near
-//!    epoch boundaries (and at most a couple of times) rather than every slot.
+//!    internally; their call sites short-circuit on most slots, so the O(V) sweep runs only in the
+//!    first slots after an epoch boundary (while the confirmed block still trails the previous
+//!    epoch), and at most once per `get_latest_confirmed` call (memoized), not every slot.
 //!
 //! 3. **Vote-root balance aggregation** (`optimizations::RootBalanceMap`): before ancestor
 //!    lookups, validators with the same vote root (or root+epoch) are collapsed into one