kinda like in gintama's second movie where gintoki has to change his appearance into that resembling a walking dick, yeon as a girl will probably look different to the characters. we, as readers, of course will see the resemblance right away (between male yeon and female yeon), but these characters can't because to them, i assume, male yeon and female yeon have distinct or different look from each other that the characters won't be able to recognize it right away, unlike us. because we're just readers.
i'm not saying yeon looks like a walking dick tho