Security devices and hosts

I've been playing with a wireghost on the team, and I'm noticing early on that their value seems to swing wildly in proportion to how many things on the map are actually hooked up to a host; last mission those were like four random fences off to the side, and none of the billion cameras.

Is it possible to predict based on the map type, and/or does it tend to increase with power level? I'd rather take a regular hacker + more utility when there's not much to skipjack.