The DJI Spark is my first quad/drone, and I'm loving it! I bought the fly more kit, and the RC has been very reliable in terms of connection. The farthest I flew it out was around 500m away at 100m height where I started to recieve some intermittent video reception issues.
Enjoy a look at the west coast from Vancouver Island through the eyes of the Spark.
Great job! Beautiful. I haven't had the courage to fly over water and at the altitude and distance you did. Did you wait on the RTH warning? I too use RC only