The RTH is not a big issue in this case since it does take off from the same spot. In my experience with the Spark it'll record the altitude of the take-off point as zero so it'll come back home there anyway. But I never let it auto land there, I use RTH if it gets outside visual range (rarely) until I can see it again and then take over an land manually. Since I'm right there next to the landing spot there's no issue in daylight. In the dark on the other hand the thing is not stable and it'll move sideways quite a lot. With the GPS lock and everything on green the Spark is all over the place (and by that I mean it'll move a couple of meters in any direction by itself-albeit slowly enough to make it kind of controllable )
