There is a huge variability between 2 games, even with the same settings. You can have Earth glassed rapidly, or just expand endlessly, even with NPR defined from the start, depending if RNGesus decides they are xenophobic or not.
That said, the initial conditions are very very important. Define more NPR at start, and reduce by half the distance they spawn e.g.
The difficulty rating alters the NPR powers, but if they are not hostile, they are not hostile ...