Since I don't know, exactly, when I'll be able to set up a simulation, I posed the question to Axiom in case they've already researched the outcome of such positioning. I imagine any performance impact would be minimal. A lot of people don't have their subwoofer drivers facing into the room, including (presumably) all people with downward-firing subs. It's not exactly the same, but then subs are often placed between furniture, so there are usually significant physical barriers in most rooms.

I know, I know. You still want me to do it so I can see what it does in my specific room. Taskmasters, the lot of you!