its hard to say whats make a person pass or nonpass able.
it can be everything from your clothing to your voice, hips or anything.
Good news is, if you know your on a low dose of T now then you can raise it alittle, and you know in time T will change more and more to make you more passable by time.
to give an advice try to have some clothing who isnt too big, to show your flat cheast and yet not something where you see too much hips.
As trans your used to shop for clothes to hide your body as much as posible to pass, as you start transition you for a time goes into a period where you has to do the opposite and shop for clothes who really show off all the maculine effects you got as much as posible.