Never did find out the correct length for mounting in that style since I found it very uncomfortable (pressing on the back).
Can't imagine why you would want to help your buddy - unless in a cave and then you would have the Ar mounted on the tanks. In openwater you would just ascend if you lost your Ar - if you were in a wreck you would retreat (ring piece clamped up - since loosing all that gas has destroyed the viz
) and enjure the squeeze of any minor descents (few meters) on your way out.
Hate the BC connection SMBs - do you guys like them?
Graham