Thanks Dave. I could do opposing corners like top #3, just with the corners reversed. My option for top #4 would have the left one about 1/3 into the room. It can't go in both front corners.One of the main reasons for dual subs is to combat room modes and nulls. By colocating the subs, you are giving up that advantage for any axial modes.
So for that reason, I strongly recommend placing them in different spots in the room. Dr. Toole did some great research on this and found the best locations for multiple subs were as follows:
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I generally tell most folks to go with one of the top 2 on the right, in the corners or on opposing corners. If you want to read the whole presentation, check out the attached PDF.