90-100 Mhs on Vii is possible not sweet spot in efficiency.
75 Mhs might be looking at sweet spot.
I've got 82mhs with lowest 850mv voltage I was able to set. (~200watt)
Do you have lower voltage so your clocks are lower and hash is only 75? What is the wattage?
I'm keeping the strategy "take the max clock from the min voltage", so I never run the card with lower gpu clock that it can handle with given voltage.