I recently got a basic kme kit along with the base, 100 and 50 grit stone. I have sharpened a few folding knives with it and get great sharp results. The thing is at the top, right along the edge is a line where the (i presume) 50 grit stone scratch patern did not hone out with the rest of the scratches. Any idea why this is happening and arn't the daimond stones all the same height?