Today I was flying in a an open field at 40ft. I decided to buzz over myself while shooting a video. I noticed as the p3 was getting close that it was more Ike 12 feet high, not 40! That instantly made me nervous because earlier, I had been flying at about 120 feet thinking I was safe above some trees. I live in a very flat low altitude area, no hills anywhere. Gps lock was no problem. I was not in atti mode. What could be going on here?