Hi,
I don’t think PC would have a different effect between AMR or legacy codecs. The step sizes and factors should be the same… The thresholds are different.
Now, you could take into acocunt that AMR is more resistant, so you don’t need to have the PC tuned as reactive as when used with Legacy codecs. This is where you have to do trials… though I doubt you’d find much improvements.
regards
pix