I have been largely presenting as male...ish... in public.
I wear nail polish because I love matching it to things. I have long hair, often in a pony tail. I still tend to wear men's t-shirts (but not always; they don't fit as nicely as they used to) and cargo pants. It's comfortable, and I don't have to think about it much.
Part of this reason is because I'm still self-conscious about any visible stubble I still have, as I'm only a short ways into laser hair removal for my beard.
But part of the reason is because I'm actually intensely curious at what point people people would start correctly gendering me.
It happened for the first time at a bar a few weeks ago.
I was standing next to a girl I didn't know and the bartender walked up, addresses us with, "Ladies! What can I do for you?"
Over the remaining weeks, it happened once or twice more. But mostly, people took me for male.
After weeks of thinking about it and observing when it happened and under what circumstances, I came to this theory:
In a group of women, I am often picked for female. They see women, and they mentally settle on my more feminine features, rather than focusing on my masculine ones.
The reverse happens when I'm in a group of men.
People are working under the subconscious assumption that groups are homogenous, looking briefly for confirmation of this, not evidence to the contrary.
(Although, of course, I suspect a factor is how well-lit a space is, too...)