Shame we are going to have to wait for CA to release additional modding tools before the battle AI/maps can be edited.
Speaking about map sizes, I think the issue you raise is also prevalent in the siege and god-awful, boring and incessantly repetitive minor coastal settlement battles. I for one am so underwhelmed by the siege maps, especially those which are meant to depict some of the ancient worlds most wonderful cities - Carthage, Athens, Jerusalem, Syracuse, Babylon, and Petra to name but a few. Half the time these supposed jewels of antiquity look like cattle villages with a disproportionately large stone wall surrounding them. What's more, because CA are apparently incapable of providing the AI with sufficiently intelligent path finding abilities, many of the major cities have been stripped of urban and other built up areas for the benefit of the AI.
The only city in the game which has any sort of scope or awe about it is Roma on extra large: the rest just lack any sort of '
epicness'. If they can make a decent city for Rome, why not everywhere else? The irony of it is that on the campaign map these cities are cosmically large...whilst in battle, where it actually matters, they are

sized. What gets to me more is that it felt like Rome I and Medieval II had bigger and more inspirational siege maps...sad really.
I honestly cannot wait until map tools are released so that people can get to work on making some truly great siege maps and can get rid of those crappy minor settlements.