Of all my 3-point attachments, the Box Blade has been the most challenging to master. Small changes in the top link controls large changes in box blade cutting depth and efficiency. Be persistent in using the BB and your skill will increase. Anything over 2 feet above level, recommend either till, or disk or plow to loosen the soil and make everything easier. Many rental companies can provide those attachments for a cost effective week long rental.
Originally, the majority of the highs and lows in my field never exceeded 6 inches, but eventually over time, i got it down to where I can see the highs if they were just 2" above level. Repeated dragging will provide super positive results.