Leak rate vrs time in large leak

Yes. I think based on your description of the facial features (sunken cheeks), some type of pillow or hydrid interface is your best approach.

As Muse indicated, the Hybrid is more adjustable than the Liberty ... especially with height between pillows and oral cushion which will likely factor with your patient.

I would keep trying with hybrid because of high pressure settings and potential for mouth leaks.

I recall in the past that someone actually changed the shape of the hard plastic oral cushion frame by gently heating with a propane torch and bending it to change the curvature. If not too much change in curvature is needed, the actual silicone cushion can be trimmed along the flat edge part where it slips into the frame to change how it fits onto the face.

Drastic problems require drastic measures or mask modifications ... something the members of this forum are good at..