For M60s I found I needed at least 2 feet between the back of the speaker and the rear wall before the bass sounded right. My understanding is that M80s need even more in some rooms.

How far have you pulled them out so far, and if you haven't tried >3 feet between speaker and any walls could you try ?

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