21' 13' room: long wall vs. short wall placement

I know there is only one real way to find out but do you think I would have success setting my system up the long wall and sacrificing the distance behind speakers - that is so important with Avalon?
Given the furniture and cabling to rearrange, I would first like a consensus from those who tried and succeeded that way.

Long wall placement has worked best for me with large McIntosh LS360 speakers and even my smaller Cary speakers. You may need accustic panals on your back wall behind you.

Nsgarch has a valid point for keeping the speaker well away from side walls.

As long as the difference is at least 7 milliseconds (if my memory still works

Bob Katz (recording engineer for Chesky) recommends about 5 millisecs....so in practice between 3 and 4 feet of distance between speaker and side wall is a good rule of thumb.....if this means you need a long dimension then it may be the way to go.
My room is just about exactly this dimension, and after a lot of playing around I have ended up on the short wall with the speakers pulled out about 3 feet from the back and side walls, and about 7 feet apart. I sit about 7 feet away, so basically near field listening. Slight toe-in. Imaging is great.

I do like the long wall idea but I agree with the poster above that the room would need to be bigger.