Baseline (Widescreen) Solution & Issues
The game is Vert- out of the box.
Resolution fix: Go to ...\Steam\steamapps\common\KillerIsDead\KidGame\Config\KidEngine.ini
and edit
ResX=2560
ResY=1440
For the FOV correction, use Flawless Widescreen to get it Hor+ or make the following INI edit:
Go to ...\Steam\steamapps\common\KillerIsDead\KidGame\Config\KidEngine.ini
Look for AspectRatioAxisConstraint=AspectRatio_MaintainXFOV --> AspectRatioAxisConstraint=AspectRatio_MaintainYFOV.
Additionally, the fade-out fix can be used to fix the cropped cutscene fade-outs in anything other than 1080p 16:9. Extract the files to \Binaries\Win32\.
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Same solution as in Widescreen but the Flawless Widescreen solution fixes the FOV and HUD scaling much better.
Eyefinity / Surround Specific Solution & Issues
Same Solution as in Widescreen but the Flawless Widescreen solution fixes the FOV and HUD scaling much better.
4k UHD Specific Solution & Issues
Same solution as in Widescreen but the Flawless Widescreen solution fixes the FOV and HUD scaling much better.