[ecomodded]

I put a top of rear glass roof spoiler on my N. Beetle in anticipation of giving the air passing over the roof a point to exit my car, rather then going half way down the back glass causing lift and increasing drag. I was thinking if i continued the roof spoiler down over the sides 6 inches would stop more air from being sucked along the body to its departure point which is not defined and has no trailing edge. I want to give it a clear departure point across the roof pillars on my car.
Any thoughts or advice on my plan to extend the roof spoiler would be appreciated and helpful, I do not want to make matters worse if this idea is more harmful then good.