Mismatched caliper pistons???

The seal rollback is a bit different between a phenolic piston and a steel piston (they also have different friction coefficients on the seal). I'd pick up another steel piston caliper. They aren't that expensive.

I had phenolic piston calipers on the Duster for a few years, and then I swapped back to "front mount" calipers since I have the hotchkis UCAs and sway bar. The steel piston ones seem to respond better and also have less roll back, so the brakes feel better.