I know someone who has a 7-40 and 7.2 flush mounted (it's actually on a pull and rotate STB bracket for service access in specially created cut out in a wall - There is no acoustic trickery, the ports just fire straight down onto the flat surface...
Looks great, sounds super. I think the bass is slightly enhanced by this actually.
There is approx 10mm clearance around the edges of the speaker!
Hope this helps.