Hello happyjohn,
Do you have your QS8s mounted at the sides of the listening area, with the "null" of the angled drivers firing across the room more or less toward each other?
If you have them at the rear of your room, you may notice a distinct improvement by moving them to the sides of the listening area, which is where Dolby Labs intends them to go and where I prefer them. In lots of rooms they'll work well moved towards the rear, but in others, side mounting improves the reverberant soundfield significantly and thus the sense of envelopment.
Experiment by moving them slightly forward of your seating area, or slightly to the rear, to see if you get further improvement. I don't think it's the height of your QS8s per se that's causing the problem, but every room is different and experimentation in surround placement is always useful.
Regards,
