Would it be possible to make it so the AI tries to break line of sight when attacked with ranged weapons if it would take too many turns to reach the player, then stay put for a couple of hours?
Other than extremely mindless enemies, most creatures can reason “I’m getting hurt, better hide.”. Similarly, many can reason “That other critter just dropped dead. Better bolt.”
This would make it so the player may need to close in on his targets once they have been alerted if there is abundant cover near them. Benefiting melee monsters that currently like to walk up to the player out in the open while being pelted with bullets.