Something that occurred to me - I've noted that whenever acafan is taken to mean something like doro's definition 2, it doesn't seem to be quite as broad as "any fan who is also an academic". I'm a maths graduate student and have never had the impression that anyone is thinking of maths/science/etc. academic fans when they say "acafan". Acafan seems to be restricted to academics in the humanities, or possible even more specific than that.