Thanks for the input everyone.
I should have lots of room above the speaker for the top firing driving.
I walked into the basement last night, and I realized I forgot one detail. Where the left surround would be mounted on the soffit, there's an extra section of lowered ceiling which houses a pot light. I think for that side I'll have to go with a FM Ceiling B otherwise that speaker would need to be moved in about 2 feet. That side would end up being a bit lower because of this.
I'll post some pictures when I get a chance.
