I'm small but I dominate great big male pupils all day long through force of character, the role I have in front of them and and little teacherly sarcasm.
On a personal note, I love to feel little (and secure and feminine) in the presence of my tall Master, but he's never once used his superior strength to make me submit to him. In fact, like a lot of tall people he can stoop, and his affable diffidence (outside of the punishment room) I find incredibly endearing.