[Suhiir]

A lot has to do with the way the AI places it's units before the battle actually starts.

I believe Don said it's basically random placement of formations.

If they're spread fairly evenly across the map it's a general assult.
If many formations on one side of the map it's a attempt to flank you.
Etc.

This is (of course) modified by to location of the V-Hex's as Gila noted.

Also any "recon" type units the AI has will bee-line for the nearest V-Hex, if they spot one of your units then the Ai now "knows" where you are any may convirge.

All this said ... yeah it's fairly predictable ... but on occasion it tosses a monkey wrench or does something brilliant. Goes back to the old saying that if you give a monkey a typewriter and enough time it will eventually write Shakesphere.