Default and current resolution

I’m trying to display the games current resolution in one of my menus.

To set the default game resolution on first launch I created DefaultGameUserSettings.ini in MyProject/Config and made sure the resolution values were set in the file:

[/Script/Engine.GameUserSettings]
bUseVSync=False
ResolutionSizeX=800
ResolutionSizeY=600
LastUserConfirmedResolutionSizeX=800
LastUserConfirmedResolutionSizeY=600
WindowPosX=-1
WindowPosY=-1
bUseDesktopResolutionForFullscreen=True
FullscreenMode=2
LastConfirmedFullscreenMode=2
Version=5

In my code I am checking the values of:

GameUserSettings->GetScreenResolution();

and

GSystemResolution.ResX
GSystemResolution.ResY

When I launch as standalone game, GSystemResolution and GetScreenResolution() return different values, and neither value matches what I have set in DefaultGameUserSettings.ini!

Which value should be trusted for getting the current resolution and how come it’s not working for me? Also, which INI file should I save the new resolution to once the user changes it?

In a packaged game, GameUserSettings->GetScreenResolution() matches what I have specified in DefaultGameUserSettings.ini, but GSystemResolution still shows different values.