One of the most important things to do, whether you shoot instinctve or gap or any other aiming method, is to establish an anchor that puts the nock end of the arrow directly under your master eye. If your anchor puts the nock to the right of your eye, you'll miss to the left every time. If it puts the nock to the left of your eye, you'll miss to the right, every time.

Once you figure out that anchor and start shooting down the middle, then getting the proper elevation for various distances will come with practice and experience.