And it's not a fastback, but to show how utterly BS 'The Template' is, here's a sedan.
So of course airflow would separate at the end of the roof and remain separated all across the boot lid, no? And to gain flow re-attachment, you'd need a spoiler that 'reached up' to the template line, no?
Except, of course, that theory is simply rubbish.
Note the clearly attached flow down most of the window and on the trailing edge of the boot lid...