Thank you for the exhaustive description of the problem. I realize that’s one thing that barely works on multi-monitor setups even on Windows, so I can appreciate the effort put into it.
I guess that’s one of the things preventing me from switching entirely, the other being the mouse buttons never work on first start 
But I really love what you’ve done with it. I switch sessions from time to time on my tumbleweed to check progress, and it feels fantastically smooth most of the time.