I am having the same problem with the first hit being soft then they pump up after that.Last year I did the wilwood up grade on all four wheels. I have the 4 piston setup all around. I am using the factory master cylender which I was told is 1 1/16". Wilwood told me this was suffice. My pads also look like the retract a little to far. I was wondering if you could use a residual or not with disc?

It will hold some line pressure in the line, might
be enough so you dont have to hit the pedal a second
time to have it feel firm but you have to make sure
they are pulling back off of the rotor

You should have a 1-1/8" MC with aftermarket 4 wheel disc brakes. WW pistons going back too far, first pump on the pedal feels soft - hmmmm.............I wonder if they copied Aerospace's fully retractable piston design. I do not remember any older WWs having this issue.