extra reduction for very likely fail high

test r15

Rapfi/search/ab/search.cpp

@@ -924,6 +924,8 @@ Value search(Board &board, SearchStack *ss, Value alpha, Value beta, Depth depth
     // Fail-High reduction (~50 elo)
     // Indicate cutNode that will probably fail high if current eval is far above beta
     bool likelyFailHigh = !PvNode && cutNode && eval >= beta + failHighMargin<Rule>(depth, oppo4);
+    bool veryLikelyFailHigh =
+        !PvNode && cutNode && eval >= beta + 2 * failHighMargin<Rule>(depth, oppo4);
 
     MovePicker mp(Rule,
                   board,
@@ -1076,13 +1078,15 @@ Value search(Board &board, SearchStack *ss, Value alpha, Value beta, Depth depth
                 extension += (distSelf <= 4 ? 0.20f : 0.05f);
         }
 
-        // Fail high reduction
+        // Fail High Reduction/Extension
         if (likelyFailHigh) {
             if (ss->moveP4[self] >= E_BLOCK4) {
                 // If we failed high for two continous E_BLOCK4 moves, extend rather than reduce
                 if ((ss - 2)->moveP4[self] >= E_BLOCK4)
                     extension += 1.0f;
             }
+            else if (ss->moveP4[self] < H_FLEX3 && veryLikelyFailHigh)
+                extension -= 2.0f;
             else
                 extension -= 1.0f;
         }