Surround speakers in crown molding

[critter]

I have a 13'Wx19'Lx9'H room that will be a dedicated media room. I'd really like to do 7.1 surround, but one rear wall has a large window. I won't be able to put a side surround there unless it's near floor level or in the ceiling. I'm not fond of either option.

I'm going to put 8" crown molding around the ceiling. I just thought of taking out a 32" section of moulding 4' from the back wall, inserting an 8"x32" baffle with 8 small 4" drivers possibly coupled with 4 or 8 small tweeters like the Dayton ND20's.

I'd expect the front half of the room and the rear corners to have poor response from combing/lobing. Assuming I could come up with a crossover/eq to get a reasonable on axis (sitting in between the speakers) response, how far off axis could I get before it'd really go to pot? I'd think that 20 degrees would cover at least half of the room. Are there other serious drawbacks of centering a surround speaker in a ceiling/wall corner?

Would it be better to go with a shorter 16" baffle to improve the off axis response? Or would stretching it out another foot or two be a better option than trying to get off axis working?

I'd probably use something like a Pioneer 84tx, Marantz 7001, or Yamaha 2700 to drive them.

Thanks for your comments.