Since you plan to put speakers on the short wall of a room that is basically a rectangular box, it's kindof impossible to avoid symmetry with the room. Only way to do so is place them on longer wall, shifted to one side, such that the distance to sidewalls is different.
Another way is with an across the corner diagonal setup. I've done this in a few rooms, with good success. Photo below is my current room -- very large, partial cathedral ceilings, open layout into DR and kitch. I tried the speakers setup traditionally on window wall and wall you see to the right. Wall to left (not in pic) is possible but it has big double doors out to porch -- not good from a living standpoint -- so I didn't try it.
Sounds best this way. Just experiment and use your ears.