Actually, you're both correct... there was a bunch of research done about shrinkwrapping and what is actual shrinkwrap and what is not... I looked up a lot of info on it and that's one of the reasons I incubate the way I do...
In true shrinkwrap the membrane is pulled entirely away from the shell very far down past where you mark the aircell lines... it will literally be encased in the membrane separately inside the shell...
After death, the membrane naturally dries out as there is no longer circulation of any liquid inside anymore or body heat, thus causing it to be mistaken for shrinkwrapped...
Due to a mess up of myself earlier, I could've shown you a good example of shrinkwrapping if I'd thought to take a pic... :/