Master Cylinder Question

[NAPA 68]

After bench bleeding a 1 1/8" bore C3 master cylinder (shallow piston), I noticed the rears come in a fair amount after the front. I currently have the same master on my car (59 Bel Air) and I am getting very little volume and pressure to the rears. I have an adjustable Wilwood proportioning valve on the system and have it opened up all of the way (the car is 4 wheel disc).

While this may sound like an elementary question, is there a M/C that is evenly proportioned through the piston stroke so the valve can do it's job?

In advance, thanks for the consideration.

Tim