I would say that the air reserve should be closer to the nose and mouth. Maybe around the back of the neck with the hose going to the nose like an oxygen patient. And what about O2 cartridge. Or the air reservoir could be high on the shoulders leading up the back of the neck connecting to the helmet. Small and streamlined, O2, and firmly attached so it stays put and can't be spit out. Avalung seems to have way too much surface area both on the hose and on the pack itself. The power of an avalanche would at least be able to dislodge the pack or the mouth piece.
Does the Avalung have an O2 cartridge built-in.