Now that we have consensus on adding a fourth custom-close reason (and confirmation from Community Manager @Catija that she's happy to do so), we now need to agree on the wording.
The original phrasing was...
This question does not appear to be about science fiction or fantasy within the scope defined in the help center.
Which I felt (at the time and now) is perfectly clear, but there's evidently concern that this is 'too generic and not helpful' and there's too much scope for it to be used to generically.
Any ideas on how to improve it? Suggestion from @Catija was
The media this question is about is not considered Sci-fi or Fantasy by our scope [link to meta post]