Thanks for letting me know that you did try it and expanding on some of the details you tried.
Yes, the Phoenix does stick out further that other regulators. I do find the flat can comfortable, but it does have an edge. I never found the edge to be an issue, but it also never hit me on a bad spot. We are all a little bit different.
I made the Argonaut a lot shorter than the Phoenix (there was just no way to make the Phoenix any shorter). I also made the can on the Argonaut with a tapered shape, with the hope that it would be more comfortable to most divers. Again, I was trying to avoid any edges that would press on your back.
If this is what works for you, I can’t argue with success. But I still feel that the “single tank adapter” moves the tank too far away for most diver.
Using a steel 72 with no spacer and the Phoenix may cause the regulator to stick out too far for some divers, but a thinner spacer is probably a better compromise for most divers.
I just hope must divers realize that a can that is flush with the back plate may look good, but it is not only not necessary, it is actually not as desirable. Ideally it will stick out just enough to always touch your back comfortably.
If the can is touching your back “comfortably”, the regulator will breath at its best. The only way to have it breath better is to have it surgically implanted.