[ecomodded]

It looks like it will help you fuel economy, maybe 2 -3 mpg.

I would keep its angle slight so you do not try to rush air over the end , but let it breeze over, if you get what I mean. keep the slope real gentle , like the boattails angle.

If you put a long piece of poly tube or wood on top of the kammback toward the ground you will see exactly where you are pointing the 'wing kammback' and can adjust it until the poly pipe or wood points to the correct angle.

Maybe the photo makes it look pointed downward to much, that's how I am seeing it from here.