I get them like that fairly regular. I think it's all about setting up platforms on the opposite side of the hump, abrading and getting the right hit in the right spot w/ the right amount of pressure. You got that right?
One thing I can help you with is to say, don't start your notches until almost the finish and keep practicing again and again and again. I had to take a week off because my body was so sore and I had to heal up some bruises and cuts from day in and day out of rock breaking, but I'm about to get back at it. Keep it up, good job. dpgratz