On an airplane wing the increase in downwash angle is partly what gives you more lift. Airplanes fly using Newtons Law of opposite and equal actions, etc. Slats, slots and flaps direct more air downward at a more vertical angle. Thus the vertical force componenet is increased. So the combination of downwash angle and amount of air forced downward is what lifts an airplane off the ground. These same principles work on sails.

Sorry for digressing a little.