That is the kind of "proof" I was looking for to convince me that common sense needed to be put aside! (Even the author of that patent notes the difficulty in showing the way it looks) Looking at his drawings, I would still object! but the text does describe this film characteristic so I concede. Now, back to choosing the best word to describe this... beveled or bevelled may not be the best here... anyway, thanks to everyone who stuck it out this far and esp. thanks to AgX who never gave up!
It is nice to learn something new... I will have to read those patents carefully, but it seems PE (and my very very vague memory) were not wrong in essence even if they were fuzzy in detail.