Jacques, in a 5.1 setup without back surround speakers, it's preferable to have the side surrounds slightly(maybe 2')farther back than directly to the side of the listening position. Although less significant with very wide dispersion units such as the QSs, it still helps in providing a "phantom" back surround effect on sounds about equal in level in the left and right surrounds. So yes, more like 110 degrees.

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Enjoy the music, not the equipment.