Just a little entertainment this morning.

You only have one pressure to work with which varies as to how hard you are pushing,lol. But I get what you mean; the bigger the piston, the more force it will exert on the pushpins. It's all about force times area.
But AFAIK you only have three sizes of rear WCs from Mopar . 7/8,15/16,and 1.00
However the smaller ones will jump out further and faster on the same pedal stroke.

Using 1000 psi as the line-force; out the WCs it would be 601/690/and 785, or about 92 psi average increase, per size..
The factory P-valve is pretty harsh in comparison. I can't remember what I got out of it but it wasn't much. Certainly not enough to hardly slow the tires down back there, that were twice as wide, and more,than the factory pizza cutters.
The w/cs on my combo are not too big. I would try larger but I think I'm already at 1.0, and the car stops so nice as it is, that I'm too lazy to mess with it.

Oh yeah, I should probably mention that I run 24psi in the back full-time (295s on 10s), so my contact patch may be a lil longer than what some guys run. That will make a difference too. And I run those hockey-puck-hard BFG Radial T/As.
So all in all,for you, with race tires and even lower pressures, Ima thinking to try 1.125s (994psi@ 1000 input). But again, I suppose that would depend on your friction materials and surfaces,etc.
I run the KH 4-piston jobs up front and 10 x 2s out back.With organic stuff, cuz it's easy to modulate and is easy on the hard parts.
Just spit-balling.

Good luck to you.