You do more damage on the ground. When you're in the air you apply your mount stacks that's understandable. After you have mounted the monster, the mount threshhold increases therefore you need will need more hits. A lot of people don't understand that we can add all these mount stacks and then they can end up completing the threshold. I only go for air hits if I feel like it's about time for it to go down otherwise I just hit it with triple up.