Your cards are thermal throttling, it’s easy to tell since they are not consuming up to your PL with only an offset for core. If you apply an offset the cards will use all the power it can get till the PL. If you use an absolute clock then the cards will only use the power needed to sustain that core clock.
Gigabyte cards are notorious for having bad thermal pads. I have a Gigabyte Gaming OC 3080 on which I did the thermal mod and now I am easily getting 100.4 mhs on the card.
My card I have realised needs about 245-250W to hit 100mhs, anything lower and I drastically lower my hash rate as well. Here are my settings, maybe they can help.
Also check my settings and try to set an absolute core clock instead of an offset for your core on the cards.
1060mhz on the core seems to be my sweet spot. You can try in the 1000-1100 range for your core and see which one gives you the best power draw.