Thanks for posting that, now my tests make sense.
I have tried modifying the client's memory addresses, I was able to move elements to reposition the UI but that caused the game to crash now and then.
In the meantime I have learned that the game modifies the UI's bounding box according to data provided by Nvidia's or AMD's surround/eyefinity setup. At least that happens with the DX9 renderer. The DX11 renderer doesn't do this, I hope it will in the future.
So even if anyone had an actual 48:9 monitor, the game will spread the UI accross the whole screen unlike when the same resolution is achieved with three monitors.
Lucky for me I have a virtual gaming computer running on my server and I stream it to my laptop. By attaching three dummy monitor cables I configured Nvidia Surround to serve a single ultrawide virtual monitor instead of three virtual monitors.
So when I stream to my desk with Moonlight or Parsec I end up with the same resolution as before, except with the game's UI centered on my screen. Here's my server with a few monitor emulators plugged in
Picture of the UI centered on my ultrawide monitor
The map is useable now
The only problem I need to fix now is that my 3840x1080 resolution consists of 1280x1080 segments, which as you described does allow the UI to fit properly.
Ideally I should have two 960x1080 segments and a central segment of 1920x1080 in my configuration. I guess I'll look into that now.