Currently (on my computer at least) the largest GUI scale option is so big that it overlaps with the EMI menu. In order to solve this, I downloaded the mod "Tip the Scales," which adds a slider for GUI scaling. However, it doesn't seem to work with the Sodium menu.

Is it possible to either add compatibility for that mod, or to add a slider?

You can access the Vanilla gui slider with the shift-p keybind in the Sodium video options menu. Please close this issue if that fixed your problem.