****ing bull is what this is, nothing works with any dependability. I just spent two hours in Arcturus, pop 400 mill, less than 20 USS's, not a single HGE.
I'm sure it's all a very complex calculation but I think that, basically, whenever you jump into a system the game sets a "base probability" for things happening, including USS spawns.
Once you're confident about where stuff should be appearing, you can use that knowledge to determine whether or not you're currently wasting your time or not.
If you jump into a system where you should be finding, say, improvised components and you don't find any after 10 minutes, just wrap it up and try elsewhere cos the game has obviously decided that you're going to be "unlucky" this time around.
Course, sometimes, even when you get lucky it can be annoying too.
