I have always hung mine coiled too or at a minimum, bring my mouthpieces a bit up from the hanging position and slip them into arm holes of bcd or something.Very interesting! I definitely want to look into this. I have been storing them horizontal since I haven't had the chance to make a hanging setup yet. I thought the idea of hanging them was to use gravity to pull moisture away from the first stage, which is where you really don't want water ingress. But I didn't consider what that means for the second stage...
I've been doing that because I don't like my regs hanging off the first stage and for the protection of the mouthpieces (so they're out of the way).
It's interesting if I've inadvertently been doing it right for a wrong reason.