Stanley, I hope the chin strap the DME girl brings you works.
If not, at least you already know now what really can work for you...the tape.
If your problem is like mine (and many other people) - lip air puffs - even the fanciest chin strap does nothing to stop those kinds of leaks.
Even with jaw cinched up tight and teeth clenched shut, some people still have treatment air push right on out past their closed lips. That's why some of us resort to tape to seal the lips like a dam to hold the treatment air back where it belongs.
Good luck. Hope the strap works.