I have now tried over 10 variations of front deflectors. So far the best two have been the triangle and the D shape deflector. D shape is the best and there is a basic shape physics backing that idea up:
That table also shows why the flat plate that car manufacturers use is not the best option. On that use its not that clear difference as that chart shows as there is the bumber blocking some of the flow making it little bit wedge in a way but still shape is shape and better is better.
That D shape in front is 0,6 to 1,0 percent better than triangle. which is 0,1 to 0,2 kWh difference in my test route.