I don't see any explicit attacker/defender designation in custom battle. I was at the top of the mini-map with the hatati in the tests. I repeated the 3 archers vs 3 hastati test with the hastati at the bottom of the mini-map, and the AI didn't do anything different. Since I have fatigue off now, the AI was able to rally more and make more attacks, but the archers still didn't win. Sometimes the AI would attack frontally and sometimes it would set up a flank attack. I tried the same test in RTW v1.2, and it was essentially the same result except the AI archers were more reluctant to charge the hastati. Archer kills with the arrows were less, but the AI set up to shoot from further away.
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