With higher feathering angles, clean technique becomes important to avoid "instinctive" wrist rotation, specifically dorsalflexion. The currently "accepted" technique of significant elbow flexion during paddle exit when the paddle reaches the hip makes hand dorsiflexion obsolete since the rotation to achieve the proper feathered-blade entry angle occurs through elbow flexion rather than wrist rotation.
I have read in a forum that top paddler Zsolt used to have an extended arm position throughout the 4 stroke-phases but at some point changed that to the above mentioned elbow flexion during paddle exit and recovery. In such an extreme style of constant arm extension (both arms), I think you would HAVE to have 0 degree feather angle.
A significant flexion of the top arm continues throughout the stroke to enable a vertical position of the shaft for the next stroke. That's how I understand it, I may be wrong and am sort of stating above as a question rather than an explanation, since I'm relatively new to wings.