On the Hollis the tank band and valve are secured to the BC using nylon cord on bolt snaps,
That is correct. And, as you mentioned in a later post, the line used for both the top and bottom attachment points is static line, not bungee cord. But, just for the sake of accuracy, this same system
can be used with the Dive Rite Nomad. It really isn't exclusive to the Hollis system.
. . .then around the midsection of the tank is a true bungie on a boltsnap as well
I am a little confused by this statement. I have some passing familarity with the Hollis rig, and even more with (at least one of) the people (one of whom I trained with) who consulted with Hollis in the design of the sytem. I am not aware of a bungee that goes around 'the midsection' of the tank. In fact, the manual link you provided does not indicate any such bungee. On Page 9, for example, I don't see a bungee around 'the midsection' of the tank. What I do see is a bungee running from the (manual-recommended) top, back D-ring of the rig, around the tank valve. The bungees - which really are, as Dive-aholic said, essentially the same as those used with the Dive Rite Nomad (with the exception of the Ring Bungee that Dive Rite now also markets, which is different) - are wrapped around the valve of the tank to pull it in close to the body.
Page 8 shows nylon cord on the neck and cam bands, the bungee according to Hollis own info is to pull the tanks int the body if they are on a nylon cord attChed to a d-ring
I dive this confirguration, and the bungees do, indeed pull the tank neck / valve into the body.
there is little utility in wrapping a bungee around them as the ss snap and d-ring is a fixed length
No, this is not the case. I can assure you that, even when using the static line attachment approach outlined in the Hollis manual, you will still want to use a bungee to pull the tank neck in close to the body.
In saying that the systems are different are you, perhaps, referring to one of the orgnal Dive Rite approaches, which includes 1) a standard deco rigging kit on the tank, and a choker which pulls the top bolt snap in very close to the valve, after which the bolt snap can then be attached to the bungee running under the arm, rather than to a D-ring on the chest/shoulder strap? One of the criticisms of that configuration is that - out of the water - it puts a lot of weight and stress on the bungee. Dive Rite addressed part of that concern with the introduction of the Ring Bungee, which includes a length of static line between the ring and the front bolt snap.
This is just a suggestion, and you are free to choose to ignore it, but posters like Dive-aholic do seem to have a considerable body of experience with sidemount rigging, and their comments are usually worth consdering as potentially useful information, not simply as hubris. The beauty of sidemount is that it is still very much a DIY pursuit. That leaves a lot of room for the development of differing approaches to how you configure your gear. You don't have to agree with everything that another diver says. But, you might want to consider it as another piece of the puzzle.
