Long Wall Speaker Placement: Pros and Cons?

There have been a few threads on tweaking speaker placement for imaging etc, but (at least for Magneplanars) it seems most people position them on the short wall firing down the longest dimension of the room.

Decorating and architectural considerations will now be moving my Tympanis to the LONG wall of my rectangular room (approx 18 x 25) where they will be firing across the 18' dimension of the room.

I am imagining - just a guess - that the bass response will suffer in this move which is a concern. Also, this will make it trickier to bring them out 3 feet or more from the new "rear" wall.

However, I suppose this might make it easier to move the speakers farther apart which could enhance the width of the image?

Or offer some other benefits from sitting several feet closer to the panels?

I really hope I can get them to work well this way and would appreciate any insights or advice.