Ratings of fics tagged with "Trans Male Character," "Trans Female Character," and "Non-Binary Character."
Analysis:
As you can see, TMC are the most likely to be explicit, while NBC are least likely. I have a few hypotheses as to why this might be.
1. NBC are seen as more juvenile, and are thus less likely to be written in sexual situations.
2. NBC in canon are more likely to be portrayed either as children, as asexual, or without romantic/sexual plotlines.
3. NBC are more likely to be written as asexual by Non-Binary people, because non-binary people are more likely to be asexual.
*** Note: Being asexual doesn't mean that you don't write sexually explicit works. But there are also many asexuals who are sex-repulsed. And, if you are writing an asexual character, I would think you'd be less likely to write them in sexually explicit scenarios. ***
As to the first, I can't think of a way to check this hypothesis. Let me know if anyone can think of something!
As to number two: I took a look at the list of characters most likely to be written as non-binary. The most common is an original character. However, the second most common is the canonically non-binary character Frisk from Undertale who, as far as I can tell, is portrayed as somewhat child-like. The next two are not canonically non-binary: Lance and Keith from Voltron, who are young but not children. The fifth is another canonically non-binary character: Hange Zoe from Attack on Titan, who is an adult* and is not portrayed as having romantic and sexual interest in anyone.
I would have to do more research into each of these characters individually, but it seems there is a slight tendency in canons to portray non-binary characters as young and somewhat asexual. It's a mixed bag, though, so I won't draw any clear conclusions.
As to hypothesis number three: it seems there is a correlation between asexuality and non-binarism, according to this study, which found that of the 1.7% of sexual minority adults who identify as asexual, 72% also identified as non-binary.
This is also reflected in the archive. In the NBC tag, 5.51% of fics are also tagged "Asexual Character." This is significantly higher than in the TMC tag, wherein 2.35% of fics are tagged "Asexual Character." This doesn't fully account for the difference in ratings, though.
A link to my (kind of a disaster right now) spreadsheet of data. Let me know what you think and if there's any other topics you are interested in seeing data on!
Happy Reading!
Sage
*Edited: post originally said "who, as far as I can tell, is young but not a child." Thanks to @ranbling for the correction.