Re: Rear surround placement
I shoot mine just over my head, and criss-crossed (left rear firing towards the right of the seating position, right rear, firing towards the left). I find this helps to produce the most diffused sound from my monopoles.
In the end, I'd say mount them where they look good and make the most sense (2-3' is good) and then play around with the angles. Jim from Platinum Audio says there's nothing wrong with "splashing them around a little"
(We recorded a session on placement not too long ago. I'll have that episode of the Podcast out this weekend).