Hello Cameron,
"I had always read on forums that the more you can move speakers out from the wall the better, so I have always done that."
This is misguided advice. As long as you don't put floorstanding speakers in the corners, which may result in too much bass reinforcement, most floorstanding speakers are designed to benefit from the deep bass boundary reinforcement that the floor and wall behind the speaker provide. Of course, you don't want to jam them up flat against the back wall, but the M60s can certainly be used with 6 inches clearance.
It's corners that are a no-no for most speakers except, in some applications, subwoofers.
The only speakers that I advise moving well out (2-5 feet) from the wall behind are floorstanding bipole and dipole designs (electrostatics, planar magnetics like Magnepans, bipoles like Mirages, etc) where you want the speakers' in-and-out of phase rear radiation to reflect from the back wall.
I'm pleased that you've got your M60s sounding good.
Regards,
