A few inches seems to be the minimum, and past that the rule seems to be just "the closer they are the more bass reinforcement they get".

I'm really sensitive to emphasized bass (yeah, I have an SVS, what's your point ) so my M60s are about 15" from the wall.

That only makes a difference when I set them to large and listen to music without the sub -- when set to small and use the sub I can stick them closer and it doesn't seem to make much difference.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8