Guys, the key here is not how far apart are your monitors, but rather, is the triangle formed by the two monitors and your head EQUILATERAL?
72" seems a bit long distance for nearfields, getting closer to midfield operation. Probably work OK, IF, and ONLY if, your head is 72" away from each monitor. Otherwise, you'll get TOO much spread and screw up panning decisions at least. Put them at the front edge of any shelf, maybe even hanging over a bit, to eliminate any sources of early reflections.
Boray, If you'll check back on some of my posts, you'll find your "original" idea about the mirror, only not necessarily a small one - the only other difference is, I referred to it as "one of the oldest tricks in the book", or something similar - I think Edison thought of it right after he claimed to have invented the light bulb. Same with the mono check for phasing - pick up any book from any half-assed wanna-be author on audio engineering, and odds are you'll find that "revelation" somewhere...
Damn. Bruce, for once I'm starting to think you're NOT being overly irritable... :=)