Micah, the walls used have to be opposite each other so that the output of the sub(or subs)at one wall reaches the other sub or subs at a point where they're of opposite polarity and cancel some of the modes. So, if neither both side mid-wall areas nor both front and back mid-walls were available to you, then Dr. Toole's suggested setup(again, note he said just by a "narrow margin")couldn't be implemented. The four corner arrangement would appear to be best available option. The two front corner and back mid-wall co-location plan you suggest certainly shouldn't be bad, but there's no info available as to how it would compare with the four corners setup.
