Height Speakers for Atmos

[The Duke]

I recently upgraded my AVR to an Onkyo 656 with Dolby Atmos & DTS:X support and want to add some height audio affect to my 7.1 speaker setup.

The attached pic is my layout. I currently have Front R&L and Rear R&L in the 4 corners, mounted about 1.5 times my sitting ear level. Tower surround speakers on the floor to the sides of my seating area, and center speaker on the front wall at abbout 2' and subwoofer on the floor behind the TV.

My Onkyo AVR aupports 8 channels, I currently have it configured for 7.1: Front R&L, Center, Sub, Surround R&L and Rear R&L. The speaker connection on the AVR for Rear R&L can also be set to Height for Atmos. I tired that and prefer Rear R&L

The ceiling is vaulted, going from 8' on the rear wall to 10' on the front wall. But right over my seating area is another high ceiling a "gable" that is 10', 2' higher than the surrounding ceiling. Think and upside down "V". Instead of ceiling speakers mounted flush in the ceiling I'm thinking two bookshelf speakers mounted on a screw as they would be pointing down about a 45 degrees. Would I run wires to them from the surround speaker connection, or Rear surround?

The other option I'm considering is instead using 2 upward Atmos speakers on top of the R&L Front speakers. Would Front R&L speaker connections from my front speakers give adequate height sound?

I hope this makes sense.