Since I have now three Stowasser mpcs, I am playing with various configurations, throat sizes, etc. Here is something that might be of interest:
The nominal size of the throat on all these mpcs was the same as the top of the instrument: ~10 mm. I opened the throat of one to ~11 mm and that made it more free-blowing with slightly more "presence", but it also made the top notes sharper. I glued a thin reducing ring at the bottom of the throat, with an opening of 9 mm. This has made the sound a bit more rounded, which I like, and also has the nice effect of lowering the top notes: from fingered A upwards. If you are having trouble with a sharp top end, this is a sure-fire way to flatten those notes. Since my spacer was quite thin (2 mm) it does not much change the mpc position for correct tuning. You can put such a thing in temporarily with rubber cement or whatever to check if it works for you.
Note however that if you are in tune with the mpc pushed completely in--you will no longer be able to do so after you insert the spacer (obviously). My instrument tunes with the mpcs pulled out by about 5 mm, so for me it isn't a problem.
I found this a much better solution than trying a thicker spacer to make the mpc longer, as described in my last post. This has darkened the sound, but it is much more effective in bringing down only the topmost notes.