diff --git a/experiments/EXPERIMENT_LOG.md b/experiments/EXPERIMENT_LOG.md
index 63bd07d..79bb9df 100644
--- a/experiments/EXPERIMENT_LOG.md
+++ b/experiments/EXPERIMENT_LOG.md
@@ -477,3 +477,41 @@ The structured grammars (43% of all grammars) capture real calling conventions.
 - 1129-file FastAPI has 30 diverse groups — need better grouping for large codebases
 - Malformed SOREs from raw code in symbol names — need upstream fix in code.py
 - Flat disjunctions are noisy — should we filter by grammar complexity?
+
+---
+
+## Round 12: Grammar Structure Scoring (commit `e62fffc`)
+
+**Hypothesis:** Flat disjunctions `(a+b+c+...+z)+` are CRX over-approximations — they list symbols without ordering and aren't useful for code completion or convention docs. We can filter them.
+
+**Method:** `grammar_structure_score(sore)` — measures structural richness:
+- Count dots (`.`), optional (`?`), repetition outside parens (`+`, `*`) = ordering ops
+- Count disjunction parts inside parens = noise
+- Score = `min(1.0, struct_ratio * 3)`, penalized if high disjunction ratio with no concatenation
+
+**Thresholds:**
+- **Structured** (≥0.5): Has ordering — tells you the SEQUENCE things happen
+- **Semi** (0.2-0.5): Partial structure
+- **Flat** (0.05-0.2): Bag of symbols — CRX over-approximation
+- **Trivial** (<0.05): Single symbol or empty
+
+**Results with `min_structure=0.2`:**
+| Codebase | Before | After | Kept | Dropped |
+|----------|--------|-------|------|---------|
+| Flask    | 5      | 2     | 2    | 3 flat + 6 diverse |
+| RAGSAK   | 19     | 10    | 10   | 9 flat + 114 diverse/malformed |
+| FastAPI  | 106    | 47    | 47   | 59 flat + 36 diverse/malformed |
+| **Total**| **130**| **59**| **59**| **218** |
+
+**Example kept grammars (score ≥ 0.2):**
+- `return.render_template+` (score=0.29) — Flask test convention
+- `assertNull?.parseS3Location.error+?.(assertEquals+bucket)+?.key?` (0.59) — RAGSAK test flow
+- `if?.return?.(token+x_token)?.raise?.HTTPException+?.status_code?.detail?` (0.76) — FastAPI auth pattern
+- `return.request?.scope?.get+?` (1.00) — maximally structured
+
+**Example dropped grammars (score < 0.2):**
+- `(@+Blueprint+__name__+app+append+class+client+...)+` (0.02) — Flask test bag-of-words
+- `(Any+BlueprintSetupState+ValueError+...)+` (0.01) — Flask sansio bag-of-words
+- `(@+FastAPI+TestClient+app+client+data+...)+` (0.10) — FastAPI test bag-of-words
+
+**Decision:** `min_structure=0.2` is the right default. Flat bags are noise — they tell you what symbols exist but not how they're used. The 59 structured grammars capture real calling conventions with ordering information.