Have you considered updating the theme to use relative font definitions?

More recent versions of FontForge allow relative font definitions, and the resources file that ships with it (except for Windows, a problem that will be fixed soon) has those relative resources:

https://fontforge.org/docs/ui/misc/xres.html#reference-font-names
https://github.com/fontforge/fontforge/blob/master/fontforgeexe/pixmaps/tango/resources.in

(The @CAPS@ strings in that source file are replaced with OS-specific values by cmake during the build process.)

By using percentage values as in the file above the user can scale the size of almost all of the windows by just scaling the default font, which is handy.