The same GUI Scale Modifier value scales the GUI differently for different resolutions

The game is scaled inconsistently, I have done some testing and noticed this cannot be normal behaviour.

Steps to reproduce:

1. Change the GUI Scale Modifier value to any value (such as 0 or -1)
2. Go into windowed mode
3. Go into fullscreen mode

Observed result:
When the game is in windowed mode it scales like Minecraft: Java Edition.
When the game is in fullscreen or a potential full screen ratio it scales like on a phone screen.

Expected result:
The game scales the same whether you are in windowed or fullscreen mode.

Notes:
In the attached screenshots you can see this inconsistency. I assume there is something wrong with the conditional compilation inside the scaling code, e.g. wrong #IFDEF