For what it's worth, I installed thicker c-clips that took out nearly ALL end play of my axles...barely able to slip into the axle groove. You can search for the corner carvers thread for the guy that sells em. Here is the email address fyi:
[email protected]
I can say that I put a residual valve AND return springs behind the caliper pistons and neither seemed to help knockback one bit.
My car is still being put together so I can't tell you whether the thicker c-clips have reduced knockback. I have C5 corvette floating calipers.