Anyone remembers Warlords II? That game at the time was really great and often difficult to beat. One thing I remember about the way the AI worked comes from an interview with its developer Steven Fawkner, a true pioneer of TBS games.

What it said basically was that the AI in that game  would calculate 20 times the result of a battle before deciding if it was possible to win. If it was so (more victories than losses in that virtual combat) the AI would actually move forward and try to engage the enemy. It is a better system IMO compared to the concept of a generic strenght factor, which value is not always accurate in this game. In Warlords II a player could also benefit from the same concept by asking to an advisor before engaging into a fight, the advisor would silently try the battle 20 times and then express an opinion based on that. Maybe this idea could be applied somehow, maybe the advisor could be a warfare technology to research, or maybe the AI could benefit from this idea, I am not sure at the moment but I just wanted to mention it.

Of course the Warlords series don't have tactical combat, so the advisor was probably more precise than it wold ever be here, but it could maybe be useful at least for situations where a player is supposed to attack a ruin where he has no idea o the enemy force  involved.