I used to be in the Navy and worked on the F/A-18A,B,C and D hornets as an "AE" Aircraft Electrician. The Leading edge flaps in crease the wing area by causing the air going over the top of the wing to travel farther than the air going under the wing. Imagine 2 air molicules stricking the leading edge at the same time one goes over the wing the other under. Thy will both reach the trailing edge of the wing at the same time. So in theory there will be more air under the wing and less above causing lift. The more you can increase the travel distance of the one going over the top the move lift you will produce. Hope that helps.