GO-NAD!, I have the same impression with EVERYTHING that Monoprice sells, including their TV mounts. I'm not talking best by any means, but best value.
I am almost certain that BMX has some Monoprice speakers. Give him a PM. I will also guess that he's probably installed a great variety of in-ceiling speakers, so that he can give you a subjective opinion worth listening to.
While I really don't know what kind of imaging limitations there are with in ceiling implementations, I do know that if you had bookshelves for instance, the goal would be similar to how you place the fronts as a starting poing: 60 degrees each to form an equilateral triangle with listener for best imaging.
If I was to redo my own rear placement, I'd like to try to spread the angles further. I am guessing close to a 6ft spread, and in fact I'd love to try close to double that instead. Live 'n learn.