While they have to spawn, you can be higher than 1-2k....I've had lit ones spawn as I flew over them when I was 3.5k to 4k up. My tip is to fly like a helicoptor so you're looking down and flying forwards. Only way I can do this in my conda.Ah, if that's the case that's a bit of a bummer. Still useful to know though.
Edit: Can other commanders confirm this behaviour?
With your gamma all the way up, large PoI's without light are also very obvious using this method.