I think Laird and Dave uses about 14deg.. I think the more angle may give more reach at the start of the stroke..and more power at the end of the stroke.
I think the angle has something to do with how it releases from the water at the end of the stroke.
I have also noticed a lot of guys flipping their paddles to slide the face of the blade rather than the back..and it would also give better clearance.
We need Blane to chime in and make a comment.
I'm happy with the angle on my Kialoa's... whatever they are..

DJ