diff --git a/Gradata/src/gradata/enhancements/self_improvement/_confidence.py b/Gradata/src/gradata/enhancements/self_improvement/_confidence.py
index 2270440a..69059b66 100644
--- a/Gradata/src/gradata/enhancements/self_improvement/_confidence.py
+++ b/Gradata/src/gradata/enhancements/self_improvement/_confidence.py
@@ -136,7 +136,7 @@ def is_hook_enforced(lesson: Lesson) -> bool:
 }
 
 # Graduation gate thresholds
-_GRADUATION_DEDUP_THRESHOLD = 0.85  # Near-duplicate rule detection
+_GRADUATION_DEDUP_THRESHOLD = 0.78  # Near-duplicate rule detection (GRA-217: tightened from 0.85)
 
 # Per-step compound-penalty ceiling.
 # gap-analysis/01-internal-audit.md #1.3: without a cap, a single rewrite