Takeoff from the lowest place or not?

In order to get the best results from DroneDeploy, do you recommend to start the flight from the lowest height point (so all the heights are >0) or not?
When I am flying in a hillside sometimes is easier for me to launch from the top so I can see the Phantom 3 easily, but in the resulting maps the height of many the points is less than 0 (in relation to the takeoff point)

Right now we base the altitude you will fly at from where you take off. The current problem with flying from a hill to map something much lower is that we adjust the speed in order to get proper overlap so you might end up flying slower than necessary. We will need to make some changes to the way we do planning in order to improve this. The resulting map should be fine even if some of the heights are less than zero.