Never paid it much attention, but I'd say it responds to my headspace at the time, which doesn't always match current presentation, but it's a good indicator. So if I'm sitting at home trying different hair styles in my new bra and most feminine shirt, it's usually female, just got out of work in my boring male clothes, then it's usually male, but certain thoughts are against the grain for one or the other so the proper one will say it, I wouldn't describe it as fluid though, the male thoughts are sort of obligated, and happen only because of years of conditioning. The female thoughts are spontaneous, and wouldn't have been allowed past the pre-internal voice stage of thinking before.
It's honestly embarrassing how much I freeze up if forced to be all male, close to nothing comes naturally in that state for me. I'd be rid of it tomorrow if I could realistically.
Side note, your new pic is cute @Ashley