I was not aware that had been specified.
You're right, it hadn't been.
But you never tried the arrangement that we are recommending here.
I'm not sure why that's pertinent. I do know that it's more optimal than the standard AIR2 configuration, but adds a degree of taskloading that the a longhose or standard octo configuration doesn't.
I find it to be no more task load at all. There's a button to add buoyancy and a pull dump at the left rear to reduce buoyancy. The only thing that is at all "restricted" is the PADI thing of, "put your inflator over your head and push the button." which is something I almost never do and which is something I would not expect a horizontally trimmed out DIR diver to be caught dead doing.
First, this has nothing to do with DIR. My only intent was to present the OP with some possible issues or concerns he may not have thought of or addressed.
Second, I'm not DIR.
Third, I use the corrugated hose to dump air about as much as I do the butt dump.
For a diver who is using the standard AIR2 configuration, this needs to be considered, as they probably won't be able to use their butt dump, since they'll probably be vertical.