Due to the ambient nature of the sounds coming from the height speakers I think QS4s would do just as well as QS8s in the height role. However, if mounted in that recess or on the front wall I think that even more so than in my room the sound dispersion would still be quite similar to a direct radiating speaker because most of the reflecting surfaces are so close to the speakers.
I hadn’t thought of it before but if you could mount QS speakers on your ceiling you could bring them out from the front and even side walls enough to get some really good dispersion of the sound which would probably make the upgrade to them from direct radiating speakers more worthwhile.
Just a note for those reading this. The QS speakers actually have great dispersion as surround and rear speakers even when placed close to the ceiling and other walls I think in part because they are also reflecting off the floor which tends to be far enough away to produce some good ambiance and reduce directionality. However, when placed up front their reflections from the floor are competing with the mains and center tending to get drowned out, which is why I think they benefit from having more distance from the ceiling and other walls to enhance their ambiance in the height role.
