I've been wondering about the AI lately too.
I had Spear Bracing and Formations on for the AI during the time I was fighting bandits only. After that I turned it off since they just stood there to be slaughtered. With these options off they just charged into battle, whether or not outnumbered.
Atm I've joined in with the Rhodoks to set up a sea side residence and finally appoint a butler to do my biddings, because bothering with the details of a household is no job for an upperclass lady commander.
Anyhow, with AI formations and bracing off, the AI parties do consistently form lines and engage is some kind of courtship display or medieval synchronized swimming on the field for aaaaaages before heading into battle, again whether outnumbered or not.
I don't know why I haven't tested the effects of the options separately, might do that later.
Which setting do you guys have enabled for the AI?
Do you know what the scripts are supposed to do or how they should work?
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With regard to the Rhodoks in sieges I just did a Rhodok vs Sawdi, resp. 200 vs 600, defend where I hoped to be a hero but died pretty soon so my influence was limited and the AI just slaughtered the incoming Swadi's like no tomorrow, it was just ridiculous. Proly also because the insanely stupid (attacking) AI, army comps and location (Uxkhal). My guys were even clumped together falling off the wall into the courtyard and getting back up just to fall down again ad inf. eventually killing themselves (it was like a bad game of lemmings), but the attackers just charged and died, wasn't even funny, maybe lost around 100-125 men total on the defenders side.
So despite or even considering the circumstances the whole felt quite uneven.