It’s a figure of speech. Not as technically accurate, but more practical and communicative.That's kind of what bothers me about that term. It's incomplete. If one line is the path to the ob, and the apex is the collision point, and the second line of the angle is the path off of the ob, then the angle doesn't define the path of the cb once it deviates. It's basically meaningless.
I’d go for something better if you have it.
pj
chgo