I am dethatching my lawn for the first time. I have a front mount dethatcher on my tractor. How much should it dig into the grass? I set it up so that on a level service in the garage so the tine's are 1/2 - 3/4 quarters of an inch off the ground. When I used it (on a small area) there seemed to be more pressure on the tines then I expected, and it left 'streaks' in the lawn where it dug up everything including the grass and left bare dirt. Is this normal?