I have noticed that after a few minutes of flight the height of the aircraft is usually off by about 5 feet but the vision/sonic position height is correct (within it's 9 feet above ground limitation). For example, the aircraft height indicates 10 feet off of the ground when the vision/sonic height is correct at about 6 feet when I'm eye level with the craft, as I am 6 feet tall. The height above ground is correct at 0 feet before I take off. Anyone else notice this?