The idea is that these TT entries are considered move valuable in TT replacement scheme - they are always overwriting other entries. So it makes sence for them to produce more aggressive cutoffs.
passed STC
https://tests.stockfishchess.org/tests/view/
62e4d407b383a712b1385410
LLR: 2.95 (-2.94,2.94) <0.00,2.50>
Total: 96632 W: 26045 L: 25659 D: 44928
Ptnml(0-2): 434, 10635, 25770, 11065, 412
passed LTC
https://tests.stockfishchess.org/tests/view/
62e523e2b383a712b1386193
LLR: 2.94 (-2.94,2.94) <0.50,3.00>
Total: 77960 W: 21363 L: 20989 D: 35608
Ptnml(0-2): 190, 7591, 23009, 8035, 155
closes https://github.com/official-stockfish/Stockfish/pull/4114
bench
5820568
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
&& ss->ttHit
- && tte->depth() > depth - ((int)thisThread->id() & 0x1)
+ && tte->depth() > depth - ((int)thisThread->id() & 0x1) - (tte->bound() == BOUND_EXACT)
&& ttValue != VALUE_NONE // Possible in case of TT access race
&& (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER)))
{