I am trying to cultivate my single rows of garlic using two disc hillers. I often cover up the garlic when too much soil is picked up and large chunks fall off the discs because the soil is too wet. I have to do something because we have had record amounts of rain in both April and May and weeds are beginning to take over. How wide should the rear opening be between the discs as I cultivate down the rows? Any suggestions. My rows are 30 inches apart. Thanks Chuck