Refine reduction logic based on next-ply cutoff count
Passed STC:
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 38208 W: 10076 L: 9754 D: 18378
Ptnml(0-2): 139, 4390, 9742, 4676, 157
https://tests.stockfishchess.org/tests/view/6945bb6446f342e1ec211d93
Passed LTC:
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 64086 W: 16529 L: 16157 D: 31400
Ptnml(0-2): 34, 6808, 17990, 7174, 37
https://tests.stockfishchess.org/tests/view/69479d303c8768ca45072446
closes https://github.com/official-stockfish/Stockfish/pull/6489
Bench: 2442415