Something like this? -rxboost? You can only add this in certain mining softwares, not all eth miners softwares support this and you said you using NBminer? That doesn't support rxboost for RX4*** and RX5** cards, try phoenix miner im certain it supports this -rxboost function
You can use AMD Memory Tweak XL for rxboost. Teamread+AMDMEMORYTWEAKXL gives the best hashrate on
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