Here's the collar cut, they're int he pics in the first post.
Boa, surface area is a falacy, if Shigo were alive today he'd tell you the same. At a seminar Brett Hamlin asked Shigo if it would be better to take a shallower angle reducing the surface area ... Old Shigo gazed sternly and said that's not the case and suggested he read more of his books. lol
The bottom of the BBR is the guide.
Check AS4373, also the same.