I attempted to put an M3 on it's side on a crt, OOPS, no-go. Works fine upside down however where the tweeter is closer to the screen than the woofer. There was even a thread on this forum some years ago where it was noted by Management that at least six inches from a CRT is recommended as the minimum. I suspect that that's still the case today.

If you can keep the M3s at least six inches away, you should be ok.