If the mask seals well on the forehead and the sides of the face, it won't leak - provided you keep the airspace at ambient pressure and don't go head down much. You can actually try this out by tilting your mask against you forehead, even if the mask is completely loose from the upper lip the mask won't flood. I don't notice much difference with my current mask between clean-shaven, 3-day stubble or more hair.
//LN
//LN
