everything is relative to the takeoff point as far as I know. You can fly lower than that if you take off from a hill, but only manually. Flight plan can only be programmed above the takeoff point.. and also the behavior of the bebop might be different if it thinks its close to the ground even when it isnt (like when I fly over a valley it might say '10 feet' but really be 100 feet above the ground). RTH would still go to 20 meters above the takeoff point altitude If you take off from a low spot, dont count on it climbing to avoid a hill. It doesnt work that way.
Quick question - when plotting a route in FreeFlight is the 'altitude' the actual altitude above ground i.e. measured with sensors mid-flight, or is it altitude climbed above the take-off point i.e. the Bebop will rise by the 'altitude' set regardless as to whether the ground it is flying over is much lower than the take-off point?