yeah, I wouldn't build a mini wall because it can mess with acoustics. If you don't like the idea of bookshelves on stand, then I would probably mount them in the ceiling. If you want to use the wt380idc for surrounds, I would mount them in the ceiling about 10-15% away from the side walls (or as long as it gives you some equalization between listeners). The wt380idc is actually a pretty good one because it’s completely sealed in its own enclosure and you can tilt the tweeter a bit to direct a little more towards the listener.
Also, not laughing on your ceiling height because we all have our environment limitations. I am actually asking for a reason:
https://amcoustics.com/tools/amroc?l=10&w=20&h=7&ft=true&r60=0.6
Based on your exact room size, it appears that you have a bass node at 56hz and a couple more at 80 and 84hz. If you get your subs in the room and still feel you are lacking bass, then you can add some acoustic treatments to absorb the bass. If you wanted to do this, I would call GIK Acoustics and have them make a special T55 Scopus trap (they will do this). The traps are 24” x 24” and probably around 8-9” thick. Cost will probably be around $240 each. I would buy 4 and stack them in the rear floor corners. I know it sounds like a lot ($960), but this is essentially like adding another subwoofer. The T55 scopus will actually absorb a little at the 80-84hz area as well.
I have two huge 12” subwoofer cabinets in my room powered by a 1,000 watt amplifier. I also have two sets of tuned membrane bass traps, one pair for 63hz and another pair for 50hz. It wasn’t until I added the 50hz tuned membrane traps that I had a significant increase of bass in the 40 to 60 hz area! So the size and power of the subwoofer doesn’t really matter if you have room nodes that are cancelling out the bass frequencies.
You can always do this in the future if you feel you need to.