I understand the reciprocity part. The problem here is having the entire speaker system mounted on the walls. Not the best for listening, but as far a interior decor concerns go, you know what I mean, that is the best option for me.
Everybody has to do what they have to do if there are "approvals" required to get them placed, but my 2c is to concentrate more on how to get the sound you want than being locked-in on the config (suspect that has happened to almost all of us). My take on the relative silence here means it's your experiment to make, as-proposed. The thing about whipping little drivers for bass is that they get dirty. And even OB, little drivers beam, so maybe measure/proto/check-out angling/toeing them a bit before you nail everything down. Appreciate that you addressed some of Wintermute's list, but I echo the sentiment that objectives besides OB remain unclear (i.e., when cleared for subs, economy decreases and maybe other alternatives arise). Say that you get this built and listen some--what's next--where is it headed? Can you skip-ahead by just listening to what you have in a fast/cheap proto first? This isn't criticism as much as it's intended to save you money & grief in the longer-term. In the end, it's about the sound you are chasing. If you already have that--great--repackage it for approval, but the wall proximity will make for a different set of reverberant cues than most "OB people" tend to favor. If that doesn't work for you, best to find-out early/cheaply with temporary experiments. FWIW.