I have tried various fullscreen numbers without success (I had to use this trick to get back fullscreen res after running on goggles) but the only number that makes a dif is 0 which appears split across middle of two screens - am I missing something as wont to have a shortcut the makes it appear on 3 (my goggles when connected) without having to disable screens and move windows around?
Here you can find an explanation to Unitys command line parameters:
https://docs.unity3d.com/Manual/CommandLineArgumen...
Check towards the bottom of the page at Unity standalone player arguments.
Perhaps you can use the -adapter N argument