Advanced rec diving is not quite the same as multi stage diving (that is, unless you like carrying stages around just for the fun of it), actually, besides being underwater & hopefully breathing while at it, they have very little in common. It's a brutal simplification, but pretty much there.
During the past several pages examples of where to place the SPG were given, and in the rec world, it's pretty much a moot debate, just put it wherever you like it in the end should you like to do so. Nobody got the chair for doing it wrong.
However, in the tech world, as you said environmentally narrow, there's a pretty good reason to do something in a certain & defined manner. And if people ask why these things are done in certain way & get the answer with an explanation - which they don't like/accept, who's to blame? Them or people executing tech dives and living to write about them here?
The internet is a nasty place. If somebody gives you an honest advice in your best interest, no matter how it is written, I would appreciate it.
Anyway, there's also a saying about arguing on the internet, but I'll not go into that...