Look at my beautiful drawing. The pilot is standing 50 meters above sea level at the bottom of a mountain that's 500 meters height. The phantom is 50 meters above the mountain. What is the real height? is it sea level to drone = 50 + 500 + 50? or is it mountain top to drone = 50? or it's pilot to drone= 500 + 50? Another interesting question is, will phantom 2 shown in the drawing be able to get good reception or it's impossible to fly behind the mountain and the pilot should always keep it higher?