My annoying room

Got my Rythmik F12 to compliment Sierra 2-EX's. It sounds great. I was anticipating problems with putting a subwoofer in a square room because I previously used a vented sub enclosure and it was either all boom or nothing. I did the sub crawl with it and couldn't find any solution. The F12 was a serious leap in quality, and I think being a sealed enclosure that eliminated most of the boom issue. I like the positioning of the Sierra's and their low end extension. I wasn't sure if I even needed a sub but the F12 really exceeded my expectations, adding presence to the room. Still, I know my desk and seating position being nearly in the center of the room is pretty much in a null and I wanted to see what recommendations you all would have to improve mainly the sub placement.

https://i.postimg.cc/9FZV3nDC/room.jpg