The phenolic pistons and PML Quantum Tube change sizes a little differently due to being unlike materials and get loose or tight fitting pending temperature.
What I do is sand the piston (a lot!) and make sure it slides well at all temp extremes ( sitting hot in the sun or sitting my chest freezer).
At this point pistons have worked very well for me but have noticed some substantial chipping of the raw phenolic due to landing and shear pin events. Maybe a light internal glassing would help them survive longer.
"...always interesting to me because as we know, there are known knowns: there are things we know we know. We also know there are known unknowns: that is to say we know there are some things [we know] we do not know. But there are also unknown unknowns---the ones we don't know we don't know...."