But then your "consistent area" is only a measure of THAT particular area and its conditions! what happens when that same area is wet? your results change. also, the machines are not designed consistently! Deck depth and different spindles change how many spacers you might have available, as well as caster height adjustments etc etc. If all these factors could be consistent, all the decks would be the same.
To accurately run this, you first need to achieve the impossible and eliminate ALL factors EXCEPT the deck (Good luck, you cant) THEN you must test in a variety of areas. In this industry what you want is the deck that performs acceptably in the most conditions. The best in dry grass might be the worst in wet grass, and vice versa.