There have certainly been people running single vertical M22s as centers, as well as a few double M22s or M2s, but horizontal M22s have not really passed the test. You'll get better dispersion vertically.
Mojo in his center shootout found dual M22's orientated horizontally to be exceptional. I have been pretty much set on M44's as the center channel ever since his post. Why would M44's juxtaposed vertically be better than horizontally? When situated horizontally they mimic a typical center channel. Just a question as I'm obviously not as well-informed as many people on this forum.
Center shootout
