Jason and I also placed M60s on top of M80s. The M60s were inverted...their woofers were up at ceiling level.

Yeah, there was a lot of presence there but we didn't exactly build a line array. It sounded like two separate, vertically-oriented and discombobulated bass images.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated