interesting. Yea I accidentally ground my flat scraper to a negative rake and forgot the 90 degree rule. It wouldn't raise a decent burr. When I reground the underside to give me less than 90 it worked. Now I'm talking about measuring the angle from the top bevel to the bottom bevel. That's what I call an included angle. Just so we are on the same page. You are much more in tune with scrapers than I am. I only use them in a pinch to clean up some area I have difficulty with.