Very good explanation, thank you. Few questions.
Every USO altercation (shooting or raiding) CAN trigger search mission.
Is it a single time bounded mission? Meaning they search for some period of time and if they don't find it - no more attempts are made (for this search mission).
Then next search mission can get triggered, and so on.
I understand this is probably difficult to calculate but what is the estimate probability for the search mission to discover X-Com base?
What is the probability for the any USO to discover X-Com base? Is it same as in vanilla or different?
Essentially, I am trying to understand with what probability I receive base attack after shooting down or raiding USO? Thank you.
The search-mission performed by each of the UFOs that are part of it has a finite amount of way-points it flies between. I think like 5 or 6. Basically every time they change direction they reached a way-point.
Every 5 minutes or so it rolls whether it detects your base. The chance of success for that is based the distance to your base and how big your base is (how many slots are filled). There's also a building that reduces this chance. The chance for each individual roll is not very high. But smaller UFOs fly slower and thus have a lot more rolls in total than the bigger ones. Basically you should shoot down every UFO that flies close to your base, as they are likely searching your base. The big ones you can't usually shoot down but those also have the lowest chance to find you, so it's fine.
Problem is: Especially in the beginning with the crappy small radar, chances are you only discover the UFO when it's already too late, as the radar only refreshes every 30 minutes of whether there is something. (once it was found you won't lose it while still in radar range, except if it leaves orbit of course)
Also: If the UFO is not part of a search-mission and you shoot it down thinking it is, you can of course trigger the search-mission in the first place.
With aggressive retaliation enabled the chance of discovery, when you do nothing against it, is pretty high I'd say. More than 50% from experience that they find your main-base that way.
Without aggressive retaliation, as I said the chance can be way lower depending on the location of your base. Threre are some "dead-zones" with abysmally small chance. If you are close to or between several bigger cities the chance is a lot higher.