The angle in question is the angle of the dovetail on the short side of the brace relative to the vertical line of the post
I'll need to make some drawings, the concept of the refined dovetail is somewhat complicated.
I've seen dovetails of about the size illustrated, they work. Note that holding strength here is different than a tenon. A tenon relies on relish -wood past the peg- to hold, the holding wood on the dovetail (which is on the post) is secured firmly to the post and is much stronger than relish.
sorry if this isn't entirely clear
