I will guess you mean the side surrounds for 5.1 as rear channels are part of a 7.1 system.

I would recommend the QS series which will work great no matter where you place them. I have my QS8s 90 deg and barely behind the listening position and they sound great to me.

The QS series really spreads the sound out which is what is required for good envelopment from the surround channels.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70