Do you have a database with a bunch of target lists? I guess... you kinda need to, else it wouldn't even be possible, right? Never really thought about this before.
There's actually a combination of different things going on.
Smart monsters, those spawning in the big rogue area in the west, have a chance of getting an actual long-distance target that they will then charge off across land and sea to wreck. At present, I believe these are now correctly going preferentially for low-density realms, and within those preferentially for regions without lords and/or without knights. (These are the ones that have an entry in the database.)
If they don't
have one of these targets, they'll look in their general vicinity for a non-rogue region and attack it.
This is why Sabadell, in particular, gets hit so damn hard: it borders a LOT of regions, which means monsters from almost all of those regions see it as the only
bordering non-rogue region. (And, of course, monsters slightly further away see it as a possible nearby target.)
I'm trying out a change to the system where monsters essentially see regions of high-density realms as being rogue for the purposes of targeting—that is to say, they might wander into them totally at random, but they'll never move in en masse deliberately. There was a small bug in that, that was causing some of the cases to fail to properly respect the high-density status, but I just located the source of it. It will be fixed for next turn change.
Sabadell did attract some new monsters, but it only got to 20k so far, and they quickly split up over various regions. Some to Ammando, some to Aquitain, some who knows where. They came from Eidulb Outskirts, might have went back there. At least we got a break for a few days, we got to refit, our allies went to refit, we are retaking our core regions, sure feels like a lot of pressure is off us already.
Now, if being adjacent to a ton of rogue regions was what made it attractive, and we could only make the Shrine rich enough to field decent militia, it would make a nice monster killing funnel.
Well, not if something happened there like happened to Paisly the other day. I don't think you could ever stack enough militia in any region to repel over 100k CS of monsters in one go
We were wondering, though, how do non-physical barriers influence monster pathing, if at all? If monsters want to attack Avernus and Westgard holds Ygg d'Razhuul, the only land path there, will that in any way influence their behavior as opposed to Yggdramir was adjacent to "the largest contiguous rogue region"? Same with Eidulb Outskirts and Astrum? We used to think that Ygg d'Razhuul was hopeless to hold, because all the monsters aiming east wanted to pass by there, but the monsters stopped going there as soon as we did, they never seemed to actually try to use the pass. Since then sea travel was also added for them, though.
If if the monsters take Eidulb away from Astrum, will they then just take the ferry to Libidizedd? Or can they not take sea routes anymore?
They're not prevented from using ferries, but they might very well decide to just hop on a raft at this point, depending on where they want to go to.
As far as monster targeting...I'm not entirely sure what you're asking.
At present, monsters never target realms. They target specific regions, and if they take it into their head to hit a particular region, they really don't care what's between them and it. They will charge for it in as straight a line as they can manage, until they forget about it (which they will do, after a certain number of turns).
And yes, holding that pass will now be much easier, as monsters should be vastly less interested in using it.
...For what it's worth, if you could manage to get enough people together (probably a coalition of realms would be required, starting a new monster-buffer-realm), you could cut the entire northwest section off from the main rogue area, pacifying the monsters there (somewhat), by holding Duil, Chrysantalys, Wallershire, and the Corridor of Torment.
Of course, that would probably be nigh-impossible to take, and hell to hold, but hey, life goals, right?