sensei is not an esoteric title or something like that, isn't it?
Isn't it just the japanese word for teacher? It's used in elementary school aswell as in the dojo. So there is nothing holy or royal or immortal or whatever in it.
We use this address with Japanese teachers. Or sometimes with teachers who lived in Japan for a while. But when it's used, it's used on an off the tatami.
That was a tongue in cheek comment! And yes, it's just a word for teacher and I only use the term sensei 24/7 to Japanese teachers.