If you have to pull your mpc out to get in tune, this might interest you:
I have to pull my new Stowasser mpcs out about 2.5 mm to tune A=440. That leaves a gap inside. In order to test the effect of that gap, I built a spacer to eliminate it.
What I found was that the top of the second octave, starting around A, is flattened considerably--about 15 cents or so--making it easier to play the upper notes in tune without a lot of embouchure adjustment.
If you are pulling your mpc out and your upper register tends to be sharp, it is quite easy to make a temporary spacer out of a section of wine cork cut to the right thickness. A round file or drill or whatever will make a nice clean hole in the center, and you can sand the edges a bit so that it fits into place in the tenon receiver of the mpc.
Added note: hmmm....after more experimentation and checking on my tuner, I may have been fooling myself. Adding a spacer also means having to pull the mpc farther off the cork because the mpc volume is decreased. It is not so clear-cut. If I get anything that feels definitive, I will post again...
Further: adding the insert raises pitch ~20 cents. Now pulling out again to bring the pitch down does lower the top end of the 2nd octave about 15-20 cents, but by then the mpc is almost 6 mm off the cork.