What a space case I am. I was going to mention the heading plate you're using, and the query regarding stress risers, and I got lost talking about woods. Oooooooozone!
Anyway, I would recommend at least a smooth radius on the leading corners of your heading plate to minimize the possibility of creating stress risers, if you haven't already done that. You can file the corners sharper after heat treating if necessary, but some minimal curvature there would be the strongest construction.