Yep... I'm guessing that's because you have them fairly far away from side walls. I don't have any direct experience placing M80s, just started to see some patterns with the people who felt M80s were too boomy -- they all seemed to be near to side walls and really near to the back wall.

It definitely does vary from room to room. We're all guessing here

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