Wingtip Vortex: Heavy, Clean, Slow - Why?

For a given speed, flaps will lower the overall AOA. Even in a
172 we can see this. It's the increased camber of the wing, as well as
its increased area if they are Fowler flaps, that produce more lift and
allow the AOA to decrease at any given airspeed.
The vortices are mainly a product of the tips, but the whole wing
has input. Air on the bottom is being squeezed and tends to flow not
only back (chordwise) , but outward (spanwise), and the air on top,
being of lower pressure, is sucked inward and flows at an angle toward
the fuselage. The angles are more pronounced the farther out on the
wing we go, and at lower speeds, where AOA is higher, they get bigger
overall. The air leaving the trailing edge ends up with a twisting
motion, producing small vortices all along the TE and a really big one
at the tip, caused by air spilling over the tip. Winglets are supposed
to control this spill, thereby reducing the drag caused by vortices.
Dan