Without going into a long drawn out explanation there is a reason we put our GA cars in a wind tunnel. There is also a very real reason we are limited on the size and overhang of our splitter lip. It is not because they are afraid we will create too much drag and disrupt airflow. Boundry layers and their height off the pavement are very real and have a big affect on drag. The air dam also allows you to better manage the air that enters/goes around the nose and its path. Small changes can alter the lift/downforce difference. But thats just my guess.