I think flush mounting them would be a mistake and go against the whole purpose of the design.
Looks like I had a similar issue with my surrounds and have no problem. You don't have them right above the peoples heads do you above the riser? They should be spread out to the sides or behind of the seating area.
My Qs8's are mounted to the boxed in area that surrounds the heating/cooling ducts, and my riser is about 8"+ high and I have not issues. How low is your ceiling?
Pics of when I had mansfield beech Axioms.
DIY mount with about 5" of top clearance.
Riser picture, perfect height so heads of front row viewers are not in the way.
