As long as the placement of the back surrounds is wide enough so that all listeners can hear both a left back and right back effect, the result should be satisfactory.

About 4' above ear level is within the recommended range for surrounds, but shouldn't be raised farther.

With back surrounds being used, the side surrounds should be directly to the sides of the listening position, since positioning them farther back isn't needed to help with a rear surround effect.

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Enjoy the music, not the equipment.