I do not have a 112PC or +, but the logic to me is......
Helix models a cab, speaker, and mic. All make a difference in the sound obviously.
The PC is a physical cab and no mic, they are modeling the different speakers in that cab.
A greenback in a 412 with SM57 will sound different then PC with a green back.
I see what you want, load the Line 6 "IR" (stock ones in Helix) and run that in the PowerCab, like you can with a 3rd party IR.
Good Ideascale to ask for it. Only issue is then you would have to update PCab with Helix updates to keep everything aligned, or they can provide the proprietary IR for you to load in PC.