The shape of the vane is not as important as the weight of it.
Some sailors prefer the vane to be slightly lighter that the lead weight below.
This means that the vane will search for mid position by itself. I changed it back to even the lead weight by putting a bolt onto it in the top. Consequently I now make all vanes to even the lead weight below but you are free to try lighter ones. Plywood is a very good material to use. It does not wear by the sun and it is easy replaced in any harbour in any country.