Since the ai will initially assign a target for each of its units to go after
I revise my previous statement. It's a bit erroneous to say that the ai 'assigns' a target at the start of the match. I was so confused by its moves in the later half of the game that I was stuck in a weird state of mind. It would probably be more correct to say that the ai always moves any unit not in attacking range towards the unit that it would do the most damage to. There seem to be some exceptions, such as when the unit would do 0 damage anyway, or if the unit has a rally command of some sort.
I also made another small discovery to add to this. When the ai is choosing which of your units to move each of their units towards -- I've already mentioned that it appears to move towards the unit it would do the most damage to, ie: it performs simple cross-damage calculations against each of your units and simply picks the one that would provide the highest damage -- but the ai also seems to
ignore any non-permanent buffs when performing this calculation.
To provide an example, consider the following.
You have two flying units: flying unit X with 18 natural defense is in the left corner of the map and another flying unit Y with 17 natural defense is in the right corner of the map (assume that all units have equal speed, ie: no doubling). The ai will move its bow units towards the unit in the right corner, EVEN IF that unit is currently receiving defensive buffs (regardless of whether it's from a hone or goad skill) that is making its current defense higher than that of the unit in the other corner.
B - enemy bow unit
X - 18 defense
Y - 17 defense (currently buffed to, say, 25)
|------
B-----|
|-------
\-----|
|--------
\----|
|---------
\---|
|X---------
Y |
B will move towards the one with
naturally lower defense, even if it is currently higher through buffs, whether from in-combat (spurs) or displayed (fortify) buff skills.
Since direct stat mods like Def+3 skills are permanent, these are not ignored.
This is pretty huge, since it means that you can safely buff your units without having to worry about how it will affect the ai's movements.