It would probably be a good idea to reduce this modifier to the cube root, either for all stars or probably just those above one solar mass
Mass / Square Root / Cube Root
5: 2.24 vs 1.71
30: 5.48x vs 3.1x
100: 10 vs 4.64
1000: 31 vs 10
10000: 100 vs 21
If a BH mass is selected from an even distribution from 2.5 to 10000, then changing to cube root still means that ~90% of blackholes will have survey distances greater than what a mass 30 star has now--which is enough to not want to bother with surveying.
It's not really the effort to survey that's the problem, it's that when you find something, it's probably going to be much too far away for any further interaction/exploitation to be desirable. You'll have hundreds of closer systems to explore first.
What if you decouple the survey points multiplier from the distance multiplier, and have the distance multiplier asymptotically approach some maximum?
That way the points required can still get enormous, but the distances to cover aren't so large that the whole enterprise is moot.
Its not an even distribution. Currently the progression is 2.5, 5, 10, 20, 30, 40, 50, 100, 200, 300, 500, 1000, 2000, 3000, 5000, 10000, so about half would be greater than a current 30 mass star.
I've been thinking about having the root factor increase with size, so that it still gets larger but at a decreasing rate. However, maybe the simpler solution is to change to the cube root, but reduce the progression so that only two or three exceed the current 30 mass size.