How to set a custom resolution and FOV?

I’m trying to run Battleborn in borderless windowed mode, in a resolution of 4096x1152, to fit my 3-monitor PLP setup, but I can’t get it working. The max setting in-game is 2048x1152, which is the native res of my center monitor.

I found the PoplarEngine.ini file in My Games\Battleborn\Poplargame\Config and changed “ResX” to 4096 in both places, but when I run the game, it still just shows on my center monitor, and the config file gets reset to ResX=2048. Anyone know how to make this work?