Full Screen mode not full screen? (bordered / letterboxed)

[snubz 10]

I am trying to run Arma3 at 1920x1080 on a 2560x1440 display. When I run it full screen, it displays in a smaller window, with black around the sides, as if it's letterboxed in both the vertical and horizontal.

I can get it to display fullscreen in the fullscreen windowed mode, however this is then displayed at the full 2560x1440, which hurts my FPS.

No other game, including Arma 2, fails to fullscreen at 1920x1080 with this setup. If I manually change my resolution in windows to 1920x1080 beforehand, it works fine, but I'd obviously rather not do this every time.

If it matters, I'm running a triple screen setup ... 2 monitors on my nvidia card, and 1 on the built-in Intel chip. However, I'm only using the one center screen for the game.

Thoughts?