Oh, but I am using letterbox integer scale. It doesn't change the fact that one can't input the proper window size without it also incorporating unneeded borders. I'd put it in manually to fit perfectly, but I'm honestly not completely sure if that won't cause problems for other operating systems and the way they handle windows borders.
I also am already using fullscreen mode, but not all players like it, and I certainly am not inclined to force anyone into one display mode.
2x window is an useful alternative for those who want to keep a window of the game and still see everything in detail.
I assume there's no expression similar to what I'm looking for then?