Drag car brakes

I have stock 73 disc in the front and willwood 4 piston's in the rear. I started off with an adjustable PV plumbed into the rear line and kept giving it more rear brake to the point it was eventually all the way open. Under heavy breaking on a 1/4 pass it just felt out of control in the front. When I originally bought my master cylinder from dr.diff (15/16 bore) he said that if I was running skinny tires in front I should have it on the front line. Switched it to the front and played with it and he was 100% correct. Car stops great now and doesn't feel out of control.

Someone told me after that you really need to calculate the bore size of the pistons in the caliper. Just because I have 8 small ones in the rear the 2 big ones in the front will give more braking so you the piston size. I don't know if that's correct but it seems like it was the situation I was in.