Great info Alan. I'm not surprised testing of angled tweeters did not yield good results. I would not recommend them for critical listening. But in this case, where in-ceiling is needed and placement may not be optimum, I found (in my case) the ability to aim the surround off a back wall helped increase the perception of distance from the back wall and helped the dominance of a down firing woofer near the seating position. Accuracy, not great, but for surround presence, it helped and here it will be for real fill only with the QS8 taking the heavy lifting. Again, I'd try 5.1 before going through all this, but 7.1 seems be a done deal here.
I have the Klipsch 5800 if that helps you, but the pale in comparison to the QS8s that replaced them.

Panny 3000 PJ, 118" Carada, Denon 3300, PS3, Axiom QS8, PSB 5T, B&W sub, levitating speaker wire