I have 2 rooms set up with a diagonal placement and it's worked out fantastic. If you check my system page you can see one of my rooms with speakers set on about a 20% plane to the back wall. I recently set up a small room system (in my son's former bedroom) with the speakers firing diagonally across the 12x12 room with my chair in near-field position approx 6 ft from the speakers.
I like the results of both setups and tried many, many more "standard" configurations before settling on these.
I like the results of both setups and tried many, many more "standard" configurations before settling on these.