If you are going to raise the rear of your hood, I think you should do more investigation.
As another poster was hinting at, the rake of the windshield creates a high pressure zone, which could push MORE air under the hood. In that case, you want to seal the rear edge, but keep it propped up so air can spill out the sides of the hood.
I would tape some yarn whips around the outline of the hood and see which direction they are blowing at speed. If they are getting sucked under the hood, then you are shooting yourself in the foot.