How is Force Level Determined?

How does the aliens scale? By time lapse just like how the other facs do or do they scale according to your force level?

I’ve always assumed it was by time lapse as you put it. Seems to go relatively the same in each one of my playthroughs, but maybe it’s because I’m always playing similarly.

By week 2 I always begin to notice armor mods show up and first defense + nest occur around here
Week 3 sirens show up
Week 3-4, more armor but still have weak spots and first lair shows up around here

The rest I kind of forget right now but loosely once I’m into February I begin to notice insane Haven defenses show up. Previously they were Force Strength 12 or something, and suddenly they’re 27. If you defeat it (I’m not sure you’re entirely expected to, or need to), then a Citadel appeared for me. Otherwise it eats one Haven after another. Around this time the straw finally breaks the camels back and NJ begins cleansing the world of the Anu and their (misperceived) relationship with the Pandorans, and WW4 begins. Easy sources of resources begin to dry up if you’re unable to defend the points you exploit/trade with and the game begins closing in on you. Around this time I always reach the final research and am able to find a way to the end of the game relatively quickly (though I’ve always just ended my game there and restarted instead of actually doing the final missions for what were bug-related reasons).

So for the Force Strength part of your question. There are basically two types of Havens in the world. Small Havens and Large Havens.

  • Small ones are around 4-15 Force Strength and may/may not be able to defend in January, and will be CRUSHED (by Pandorans and Factions) in February (these ones you will show up to, almost destroyed, and have a scylla, 2 chirons and a dozen+ additional enemies or something before you’ve even seen a scylla), you’re not expected to be able to defend these easily I believe, nor is it necessary.
  • Large ones are around 20-30 Force strength and will almost always successfully defend themselves against everything but the invasions that show up in February. Where if you get to it a bit late, the Force Strength will be reduced to a reasonable 10-15 and it’ll feel like a normal, though still tough, fight.

Higher FS has better types of enemies with more tricks. Scyllas or multi-classed enemies with WP abilities for example. So even later in the game you can exploit a low 4 strength haven like Synedrion because it’ll only have Assaults that do max 30dmg and are completely nullified by heavy armor/vehicles, and Snipers that are the only real threat, maybe wielding a paralyze pistol later on. But I never saw an Infiltrator. Easy peasy for 800+ resources.