Consider 500psi of fluid pressure at one 4-piston caliper.

With 1.38 pistons, the force exerted on the pads is 2960lb. total.
With 1.75 pistons, the force exerted on the pads is 4800lb. total.

Or another way to look at it - I can get just about the same amount of force on the pads with 4 1.75 pistons @ 300psi as I can with 4 1.38 pistons @ 500psi.

The calipers are not correct for a skinny front tire-big rear tire application. The front brakes are being forced to do all the work. Knowing the fluid pressure is useless without taking caliper piston bore size into consideration. If you have the same caliper on all 4 corners of the car, then you can compare front and rear pressures and get an idea of what's going on.

A lot of Stockers and Super Stockers have gone to four 4-piston calipers on the rear with either two 2-piston or two 4-piston calipers on the front. All with the bigger pistons. Then matching MC size to the total fluid requirements of the system.