i mentioned this as a possibility in a thread on the cable topic (?!?) called *excessive bass*. (?!?) any set-up that places the speakers asymmetrically in a room can be beneficial, especially for small rooms. it doesn't have to be completely diagonal - for example, keeping the listening-triangle-ratio the same, try moving one speaker closer to the back wall, or have one speaker closer to its nearest side-wall than the other, etc. this *will* help break-up standing-waves.
i have my speakers set-up this way, w/the right speaker closer to the right wall than the left speaker is, to the left wall, & my short wall is 25' long...
regards, doug