I've been playing a bit and effectively, and as far as I saw:
- By the end of the third month one country leaves and an alien base spawns on a know position on the map (at least that what happened in my last two games, I assume is intended like this).
- By the fourth month you reach negative points and have to finish my fifth but it seems it would likely be the same.
The reason seems (thankfully for the radar coverage) is that the mission "rulette" has heavy weights in supply and influence aliens mission. There was a point on by my radar coverage where USOs congregated like bees. One interceptor and several medium, huge and very huge ships congregating on the same spot (which I believe is the second base yet-to-be-found). Of course even if doing the rest of the accessible missions your rating suffers drastically from this behavior.
The problem here seems not on the difficulty but rather on the unbalance of mission weights, providing much more uso missions that you can't tackle yet instead of providing other missions more accessibles.
So that would explain why @LouisedeFuines was having troubles with interceptors and big USOs. @Nord if you can check this behavior as it will probably be the issue they are complaining. How often are these missions USO missions from the alien base generated?
I hope this helps to solve the problem they are experiencing.