Nasal interface: how high of a pressure will work?

I was able to try on different masks today at my sleep center.
I had my first try at nasal interfaces and it looks like I'm going to stay with the full face mask. So much air was leaking into my mouth that i couldn't keep it in no matter what i did with my tonge or my lips.
My cheeks were all blown up and my lips were flapping in the breeze. Really must of been a funny sight I give the nurse credit for not laughing, I was.
So just out of curiosity I was wondering if anyone is using one at a high pressure.

Mine starts flapping at 11!