Well, from experience of riding coasters (as all of us here have), the steeper the curve of a hill is, the more of a "pop" of airtime you will receive. Also, the steepness of the descending drop also can be a factor for how much airtime the riders will experience. The less steep a hill is, the less airtime you'll experience. Also, double-down hills can produce airtime as well. I hope this helps.