EDIT: Haha, looking back at this post makes me realize how many incorrect assumptions I had about

how resolutions and upscaling worked in general. As such, I decided to edit it all out as I found it hilariously

painful to read.

Nevermind, managed to solve it by making use of GetWindowLong and AdjustWindowRect like SFML does here (WindowImplWin32::setSize method):

https://github.com/LaurentGomila/SFML/blob/master/src/SFML/Window/Win32/WindowImplWin32.cpp

Sorry for the stupid question!