I've always had superior numbers (at least 5:1) when surrenders happened. Randomization seems to be present though. At times, the defenders would surrender; most times they would not despite the odds stacked against them. Unlike others, I do not find this combination of algorithm (odds stacked against AI) + randomization (there is a CHANCE but not certainty that the AI will surrender if the odds are against the defenders) annoying.
Bookmarks