I also deal with this to some degree. Lots of good suggestions here. I was able to get my speakers to disappear pretty good by moving them about 1/3 into the room. You can also move your listening position further into the room, or do the opposing corners approach with putting speakers and listening position in opposite corners. A few inches here and there with speaker positioning and listening position makes a big difference. What I did is got out the measuring tape and paper and started charting positioning and seating arrangement locations. I think I found what is best after a couple months or so of trail and error. Once it sounds really good, room treatments only will make improvements. Try to let the room dictate positioning not furnature placement...if possible. I took the approach of breaking up symmetry with placement. Speaker postion in the room, position from the back wall to side walls. Position with seating position off the back wall, speaker toe in, speaker height..... 3rds, 5ths, 8ths, etc.
Also want to mention while doing the process I was mindful of speaker volume and cut out some of the bass, since bass modes are most affected by a square room in order to obtain the best imaging. Once I found the right placement I was able to introduce more bass. I also just played bass in these positions to see what ares would overload the room to rule out those placement options.
Anyway...I am by no means an expert at all and new to this hobby. Much what I have learned is from the great knowledge of this board and other online resources, so take what I say with a grain of salt. Like you I have been doing much research on the subject and was able to get my speakers to image and disappear by doing this process in my room. Hope this helps.