the more I think about it -
maybe it's not about pronation.... instead it's about how the wrist moves.
the wrist can have extension/flexion or radial/ulnar deviation, or a combination of the 2.
if it has a lot of extension/flexion then you end up with a finish with palm facing yourself or to the ground.
if it is engaged mainly in the deviation action, you end up with palm facing the sky at the finish.
hope it makes sense.