I believe with the 24"x 10" opening that Panabrite has, he'll be fine with the ports and and his in-wall placement.
Whenever I built our room I was going to enclose a pair of 60s in the back wall for rear surrounds and was told by Axiom that so as long as I had approximately 4 or so inches of clearance behind and to the sides or top there would be no SQ loss, and with that clearance the ports would be perfectly fine. I went so far as asking if that setup would work for the mains and was told it would work 'perfectly fine'.
The dimensions of the M22s are H W D (inches): 19.8" x 7.3" x 8", so with his 24" by 10" opening Panabrite should be fine as long as there is clearance for the back of the speakers.
Beautiful setup Panabrite, welcome and enjoy!
