This is all on a 4k 32" monitor (3840x2160), but for whatever reason ShiftWindow puts it at 2560*1440 - I'm assuming that's due to 150% UI Scaling on my windows desktop.

So in ShiftWindow I have my main screen set for 2060*1400, then my smaller screens at 500*350 - which leaves room for the 40 pixel taskbar at the bottom.

Within the game, it recognizes that I'm running a custom resolution of 3090*2100 and then 750*525.