I hear you man, I really do. I experienced the same as you and argued with the sleep technician that I was a mouth breather....she insisted that I try the nasal pillow mask fiest and she was right.I went with the full because I know sometimes I sleep with mouth open.. Usuaully I breeathe through my nose, but not always.. I have a bit of congestion right now, so I woke up breathign out my mouth.
I played around with it a bit again and I can get a good fit (according to the machines test) if I use the mask to push the beard downward instead of rest the mask on the beard.
I rarely use a beard oil/conditioner, but I bet if I used a bit on the beard before bed it would let it lay flat enough for the mask
When I use the nasal mask its like it creates a venturi and suctions my mouth closed.
I put the mask on even when congested and the conjestion goes away miraculously.
I was so sceptical but relented and tried and I would have never thought in a million years that it would work. I was wrong.