As you say SirQuack, the physics can't be cheated. While I haven't had the opportunity to demo the different 22 versions as you have, a simple browse of the specs shows the differences that cabinet volume make.

Both the in wall and on wall 22's state 70Hz-22kHz FR.
The full M22 and in/on wall 22 (formerly known as the W22) have stated FR's from 60Hz - 22kHz. These two both have the larger cabinet volume.

On-Wall M5HP LCR, QS8 & EP500 in 7.1