What happens is the same as what would happen if a plane took off from the top of a high cliff and flew over the edge.Similar kind of question if I may... if I take off and hover at say 50ft.. and then fly over a quarry where the quarry floor is 400ft below... what happens to the drone? I have a Mavic Air. Does the height of the drone then become 450ft.. and now flying higher than permitted?!