I'd go maybe 100 feet away before realizing that it wasn't going to follow me. Yes I am sure that it was locked on to me because it would rotate to follow me, it just wouldn't move from its hovering position.
If you just want it to follow you I find it easier to use the hand command mode. Take off - get the distance you want - start video. Then ignore it and it follows you. Occasionally it has trouble but it usually works fine.