I just ran the math. Eight feet away, 96". Speakers are 20" wide so spaced 15" apart three M2s plus space yields 90" total across the front, 70" center-to-center for the LR speakers. I did make a mistake and thought the speakers were also 15" wide, however, so it's not as bad as I thought. Anyway, with a 70" spread, you could sit 60.6" away if you buy into the equilateral triangle approach, or about 5 feet. Three feet shy of eight feet, and so the stereo image is going to be a bit "compressed", i.e. more in front of you than desirable. Could you live with it? Probably. You could move closer, though my guess is five feet would feel too close for comfort. And having speakers closer together than they are wide may look a little funky but aesthetics is a secondary issue for many.
I have tried phantom centers on and off and personally prefer a center speaker. It helps balance the sound for more than one person by keeping the dialogue (or stage center for audio recordings in surround) a bit more "centered" for people on the ends of the couch (or whatever). For stereo music the central sound is very stable in my system, to the point that visitors often go stick their ear in the center to prove to themselves that it is off. So it can be done. Still, I feel the sound for movies is better with the center running.
I do not know his (or her) space constraints or size of the room; if that was stated I missed it. So I do not know why the close spacing, or if there is a workaround (like rearranging or reorienting the room). Nor do I know how you got from a simple calculation/comment on stereo imaging to small rooms not being able to have great audio; I certainly never said that. My room is not large by most standards and yet I think it sounds pretty decent.
As I said, in my opinion, no problems if you disagree. But please don't put words in my mouth I did not say. I say more than enough to get in trouble, don't need the help...
YMMV - Don