Just to clarify...
I have been lucky enough to have Dr Thomas Wolf, the current head of Porsche aerodynamics, reading my
Modifying the Aerodynamics of Your Road Car book.
He has been good enough to give me detailed feedback, chapter by chapter. There's a lot that he says that I'd like to add to a new edition of the book (should one happen), and a few changes I'd make based on his suggestions.
Regarding how the rear spoiler works on the early Porsche, here are the text and pics from the relevant page of the book:
Dr Wolf's comment on this page was:
"rear spoiler => perfectly explained"
It's frustrating when people take notice of those spreading theories that are quite wrong, because it wastes the time, energy and understanding of those trying to understand a really fascinating subject.