Like me.Majesty 2 helped me to rediscover Majesty.
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May be a story of AI flavour.
First time I checked, it was straightforward. Ratmen displayed the retreat behaviour. I did not investigate long as they did it fast.
Later, reading this thread, it appeared that the same settings I used did not bring the behaviour.
I tested again these settings and this time, I did not observe the retreat behaviour.
I changed the settings and observed once again the retreat behaviour.
One major difference each time:
retreating ratmen come from ruined keeps and/or ordinary dens.
non retreating ratmen come from rats dens.
Maybe rats dens spawn rats with an aggressive AI setting whereas rats spawn by another kind of den come with a venturing AI mindset.
I also noticed that from the start, ratapults were spawned.
So far, observations brought that:
rats can or cannot retreat
they can retreat to ruined keeps, indestructible sewers and pipe sewers
they dont retreat to rats dens.
Might make sense as rat kin coming from any other lairs than rats dens are residents or something and rat kin coming from rat dens are native to the territory and display a territorial defense/repell the invasion mind set.