Arch,
I didn't think it'd be you who would immediately bring up another scientific
versus reality topic?!!
I agree with all you said and Cindy Drozda agrees, too. Only she swears it
makes the difference between white knuckle work and pleasurable turning; and
can't tell you why but it works!
Cindy did a demo around here about a month ago and boxes are her specialty -
end grain work. I'd have to go back to my notes to see what her bevel angle
was but the "negative rake" angle I recall was about 5 degrees off the flat
of the scraper.
I just did a box today and used a scraper lifted off the rest so as to get
it to work. Hell, maybe I created that "perfect" angle and the difference is
that they get to keep it flat on the rest and parrallel to the ways at
center point.

I'll tell you one thing I tried today that worked SWEET. Bill Grumbine in
his video and Ellsworth, too, have this thing of bringing the wings of your
gouge up about 45 degrees to the rest and the wood, then barely cutting into
the oncoming wood. Put your sandpaper away. First do the Ellsworth thing of
scraping with the lower gouge wing to get those fine sweeping, rutless,
curves and then get that great finish shearing at 45 degrees to remove that
last little end grain tearout. DON'T be aggressive or you'll get hurt.

I guess you can't
have a scraper's edge without two surfaces (bevels) meeting somewhere.
Does their included angle determine rake? If I tilt the flat top
surface that completes my standard scraper's bevelled edge downward with
the handle upward and the edge kept above center inside and below center
outside do I have in effect a negative rake scraper? With a lantern
type tool holder I can change top rake on my metal lathe without
grinding the bit.