I may be missing a point here, but my recollection of driver design is that a driver can be made to work best with the kind of acoustic suspension offered by an enclosed structure, or that same driving mechanism can be designed to work best with no enclosed volume behind it. In the latter case the physical suspension of the driver (spider and surround) "tunes" the speaker for best performance.

You'd get the best performance out of a speaker installing it with the rear volume for which it's designed. Since in-wall and in-ceiling speaker instructions don't tell you to create a box behind them with some particular volume, I conclude that they're mostly designed for open back use.

I could be wrong.