Silly Resolution Question

[AdamvsMaximvs]

Hey Everyone,

My monitor's a 3440x1440 21:9, to try and get a little better performance from Oblivion, I've droped the resolution to 2560x1080 in the ini. Fullscreen is enabled (both in ini and in the oblivion reloaded ini)

Ini is like so (and is proper fullscreen when set to 3440x1440)

bFull Screen=0

iSize W=2560

iSize H=1080

iAdapter=0

OR ini is like so

[Main]

WindowedMode = 1

FoV = 90.0

But the 'fullscreen' mode only fills the top left corner of my monitor (ie only 'fullscreens' the upper left 2560x1080). In some games alt+enter can fix it, but I know oblivion's a little old. Is there a way to either trigger oblivion to to the screen stretch alt-enter or to have it change the screen's resolution when running or am I pretty much stuck changing my native resolution to 2560x1440 anytime I want to run the game in real fullscreen?

Hoping there's something simple I missed, but if not, I guess I'm going into the control panel before playing haha.