I think the main issue is optimizing symmetry forward of the listening position. If both short walls are perfectly symmetrical left to right, and in either case, both right and left walls are perfectly symmetrical forward of the listening position, then put the window behind the listening position. In a room having these dimensions (I'm assuming 8 ft ceilings) you are going to have some challenges. 11 ft is a bit narrow for good imaging, but it can be done. Treatment of the corners will be important, as will treatment of the front and rear walls. Front wall treatment will probably be mostly low frequency absorption (preferably limp membrane type panels) and back wall will be aimed more at addressing early reflections. I would opt for absorption rather than diffusion in a room this size. I can provide more details if you want to take the discussion off line.
