Target sorts only go up or down in priority. Using a value of 1 will prioritise units with 1 or more height going for the highest units first.
Contribute to the wiki (Wiki button at top of page) Considered easy altering of the unit textures?
With regards to your problem about it not shooting for a while check the Stats: Damage Point of the weapon.
In reply to DrSuperEvil:
Determines the time from acquiring a target until it starts firing.