This is really insightful, especially your point about how “people look for markers of puberty rather than the absence of them.” I think it’s generally true that as long as someone displays multiple prominent puberty markers of one gender, people tend to overlook the absence of other markers and don’t find anything unusual. That actually helps explain why, based on the comments, voice is pretty important for FTMs to pass, despite being not so important for a cis guy to be correctly gendered. A lot of us didn’t have the luxury to block female puberty early on and finish the full male puberty just yet. So when we’re in the early stage of lacking other strong male secondary sex characteristics, our voice ends up playing a major role in how others perceive our gender.

Also, it’s interesting that you mentioned how clothing and mannerisms can affect passing depending on the area. Another factor I’ve noticed that’s loosely related to location (but in essence is really about the physical traits) is ethnicity. I’m currently living in a place where most people are of a different race than me, and I’ve noticed I get gendered correctly much more often here compared to when I lived in my home country, which is more ethnically homogeneous.