I am just guessing from my experience of making scales and watching how they work. Glen got me to thinking more about that in one of his posts about wedges. On the other end is the tang and I believe an angle/wedge design there helps keep the scales off the blade and tang. I also believe it helps with the pin to keep the scales tight. If it were all just flat the first sign of wear and the pivot would be loose. A little bit of spring pressure from the scales prevents that. When honing you don't go past the shoulder anyway. Bruno knows a lot more about blade geometry than I do and as I said I am just looking at how things work from what I have seen and I'm guestimating. You got me to thinking is why I ran out and measured :<0) I am putting some finishing touches on my first RSO tonight and will post it for comments and suggestions later. Good luck with yours, I will be going along for the ride.