I've used a dmt e only to sharpen knives and the dmt c for razors. I know I am lazy. But after you mention the C not leaving as deep a scratch as others works in favor of the theory. See according to my mental experiments, all I do with the dmt C is cut to planes that meet, then I refine with the coti. So if the scratches aren't deep and the coti cuts shallow marks as well... well it all seems to fall into place. I do use tape on the spine when doing this for those wondering.