Rather sure being Potions Master and Potions Teacher are the same sort of niche. The Dark Arts, for example, would be a different sort of niche.

[James can't help himself. Harry's told him all about that. And while he's trying to be fair for the sake of their shaky truce and this unfortunate memory, Snape is such an insufferable git that it makes it all very difficult. And they call him arrogant? Merlin.]

Headmaster is as impressive as it is shocking.

[Those poor students. Really.]