The maximum engagement ranges are increased: AI will fire in bursts with variable lengths on high ranges of 500 - 700 meters, depending on their weapon and optic.
Some weapons had minimum engagement ranges. If you were as close as 2 meters to an AAF soldier, he wouldn't open fire, because the AI couldn't find any valid fire mode for their weapon. ACE3 removes this behaviour mostly notable in CQB by adding a valid firing mode.