Here are two more pictures of my current listening room showing the missing view of the other rear side of the room, plus the view of the ceiling. I could only attach five photos to my original post.
The ceiling photo is looking up at the ceiling from behind my listening seat. It shows two 2-foot by 2-foot sections of 4"-thick Sonex balanced atop the fan blades. These pieces of Sonex were placed so as to absorb the ceiling reflection of the speakers as seen from the listening position.
I obviously can't use the fan like this. I had every intention of permanently attaching the Sonex to the ceiling, but this arrangement worked so well sonically, and stapling that Sonex to the ceiling while holding it above my head and avoiding the fan blades seems like such a daunting task, that for now I've decided to leave it just like it is and forego use of the fan. The several inches between the back side of the Sonex and the ceiling surface may actually make the Sonex more effective in terms of absorption at lower frequencies.