Fictional Fans

(This is also a definition that requires you to come up with some kind of defined "work" an RPF author is working from, which is also difficult to do.)
Yes! I have an exchange comm that doesn't take RPF just to avoid the flames about hat is canon and hat is not (and it includes historical RPF, biographers often have wildly different takes)

To me if it's just yourself you have actually a total control over your audience! So it's fanfic if you're writing to pleasantly go back to the universe, and not fanfic, if you feel like it inspired you to do your own thing (even if it looks like fanfic from the outside)