bigger rear disc in rear than front a problem I assume?

inertia said

What's the piston/puck size front and rear.

Smaller pistons rear is like running smaller diameter wheel cyls.
Proportioning valve adds overall adjustability with weight load etc .

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Finally, someone understands and offers to chime in.
You could have rear rotors twice the size of the front and it wouldn't matter as long as the caliper size is proportioned right.
A common guideline for a 4 wheel disc system in a well handling car is a 2 to 1 brake bias, front to rear.
You want twice the caliper bore surface area in the front compared to the rear. Rotor size does matter some but it is the clamping force of the caliper that determines the actual braking capability.