Some modes make headings appear larger and other things appear smaller (adoc-mode being an example) — does anyone happen to know how/if that kind of thing can be disabled?

@martinklepsch Typically you have to override all the faces the mode defines as scaled in some fashion. Generally there are no global settings you can update, as everyone’s doing their own thing.

In zenburn I simply override all the adoc-mode faces with ones that always the same size. You can take a look there and do the same for whatever theme you’re using.