It's always best to shoot for the lower third of the vitals whether shooting from the ground or an elevated position. You should be able to hit the same from up there as from the ground. What you have to do is bend at the waist, keeping the same upper body form, and aim where you want to hit. Most people who hit high from elevated positions are not bending at the waist. If you don't practice it it's not all that easy to do on the real close shots.