It's not science, it's linguistics. Trans ppl refers to a social construct related to gender roles. Crossdressing is a fetish related to your gender.
Not all trans ppl would be considered crossdressers even by your definition.
Even so, you're still gonna end up confusing ppl. If you're looking for the trans specific fetish, that's sissification, futinari, and transexual. Be advised tho, transexual in this context is a slur tho.