I was half joking, as I assumed you were talking about boards. I don't use boards so for me the back is dictated by the back that is given. The only thing I might do on whitewoods is trap the sides so that the back is more narrow than the belly but that is because I have not the experience with heating treating that I want.
I cut the belly as flat as I can with a large rasp and scraper then I round all 4 corners off, to some degree, to avoid stresses there. By the time I round the edges with a tool, and then sand the edges, the belly is no longer flat but has take on a slight radius.