Playing a game where I had the setup to 40% generation from the player and 15% from other NPR's, 1 NPR on start and all other setting the default (min 25LY and 50Max). So far I am 80 years into my game and the only Aliens I have met are precursors (4 of them so far). Given I have 91 systems and 71 of them are surveyed its getting a little boring not having anyone to face. This is the second game in a row where this has occurred and I am wondering if I am doing anything wrong. I was expecting to come across other "Empires" to fight.
The chance of discovery by NPRs is very uneven. I remember seeing several posts where people get discovered by an NPR within the first ~5 years of a campaign, even with higher than default starting distance.
For your game I would increase the player-NPR generation to 70-90%.
This is because of how rare suitable NPR planets are, if you find one then you want it to spawn an NPR, with a small failure chance to add some uncertainty (this is less necessary if, like me, you don't know the parameters within which NPRs can spawn).
I would also reduce the NPR-NPR generation to 0%, and turn off NPRs trigger spoilers.
This is to ensure that the starting NPR doesn't get tied up in a war, and can put as much effort as possible into exploring and eventually finding you.