You are on the right track about needing bigger master cylinder to compensate for brake travel on larger pistons calipers or otherwise the pedal does go to the ground.

I don't know the equation of the fluid dynamic but cracking open a brake handbook should yield the info. I will check my Bosch handbook later tonite to see if they mentioned anything about this.

The smallish piston on multiple pistons caliper means more contact area on pads and thus more force on the greater area of the brake pad and thus better pad perfomance and better braking. As your website said, the balance of the front and rear braking performance is very important.