‘Lift is caused by a flow deflection of the airstream behind the airfoil.’
Ignoring the error in the above statement by using the word “behind” the airfoil, obviously lift cannot be generated from behind the surface in which the lift is being generated perpendicular too.
The air flow in the shaded arrows are a 2D representation of the Flux Rope Tube above. The manipulation of the direction of travel can be seen around the double skin foil. This explanation holds true for single skin foils such as yacht sails, which use a single layer of fabric to generate lift perpendicular to the curvature of the sail cloth.
Lift generated by a yacht’s sail is largely ignored by high school physics teachers when discussing the incorrect theories on lift that have been proposed thus far. The 3 most common have been disproven by NASA, yet this is generally not discussed in textbooks.