There have always been questions and issues about a DH compatibility with many back packs. Part of my design goal with the new Argonaut case was to make it compatible with as many backpacks as possible.
During my recent Maine-iacs club pool session I had five DH regulator set-ups with different regulators (mostly Argonauts) and several vintage backpacks, plus my backplate.
Afterwards I decided to take some pictures of the fit.
Notice that with an AL80 there is plenty of room. With the narrower ST72, the regulator fits with both the thin plastic backpacks and the blow-molded backpack, but there is no room to spare. The best fit , as expected, is with the plate.
The pictures shows the fit, but regulator position also has to be considered. I dove the Argonaut with both blow-molded backpacks and the performance seems fine, but there is no question that the blow-molded backpacks separates the regulator a bit from your back.
From a performance point of view, based on my observations, the VDH backplate is the best. It holds the regulator in the correct place, actually touching your back, and it holds in place better than most other types of backpacks or harness. Other thin backpacks and some of the modern thin synthetic back packs (like the Express Tech) are very close and work very well.
I actually also really like the thin contoured backpack that I am showing. It is just very comfortable to me. That is the Nemrod type with the somewhat flexible plastic, that doesn't break like the US Divers did.
