A full or nearly full convex grind would start near the top of the blade. Some start midway, some further down. If you have a knife that already has a machine grind, saber, hollow, or flat, and you try to do a thin convex edge, the belt will make contact with the primary grind line and the final edge, leaving coating in between. This doesn't look too good, so I make my convex grinds on coated blades less acute than a factory convex grind. They are strong sharp edges, though, and cut very well.