I pull a 6 foot STH with a NH TC40DA. Works great in my rocky soil in NE PA, almost too well. Even when I just want to scratch up the top 2-3 inches of ground, STH will dig deeper and pull up more rocks. If I feather it up slightly for more shallow pass, it usually rises to surface and doesn't do any tilling. Unfortunately, I don't have draft control. I was trying to think of a way to keep the depth shallow, but couldn't come up with one. Any thoughts??