I don’t see the reference you mentioned from Randy…
Yes, it’s all about the angle of departure from the vertical of the surface being machined.
I was beginning to do a detailed write up when I remembered I had seen an article on parallel, waterline, and pencil finishing somewhere. I went back into my notes and found it. Here it is:
I think this does an excellent job explaining things. The 47/43 degree setting should now make sense. The default values are pretty good; @Randy does it better.