Blackie, welcome. If I follow, you're discussing two QS4s, not four. If your couch is just a foot or so from the wall behind, your QS4s can be mounted effectively on the back wall about 2-3' above ear level. They continue to be side surrounds in a 5.1 setup, even if mounted on the back wall, and should be separated more widely than in your illustration, almost to the side wall on the right and a similar distance to the left.

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Enjoy the music, not the equipment.