how to make my 6800’s run properly

hey everyone, tying to mine rvn with my rx 6800's but i cant get the power down without tanking my hashrate. adjusting the voltage% (lowering this causes me to crash) and the power tuning doesn't do anything, the only way i can lower power draw is lowering core clock which sends my hashrate to the floor(around 28-29 mh/s all the way down to 21-22 mh/s). can anyone with the same cards (rx 6800 non xt) give me some tips? im using nbminer on windows and the amd software to tune the cards. any help is appreciated.