JNI, as what I've observed from the game's units, they're.. dumb for instance, they just follow an enemy in a certain location and shoot at it. I'd suggest you the following (please read every sentence so you would understand):
First: Sensitivity
The units are so sensitive when it comes to enemies, example: An enemy is inside an area where no one can possibly see (in the point of view of the units) then the units are destroying the building without even sensing the enemy; the units should only kill enemies only when they see or hear them shooting. And another thing, the units are insensitive, example: I shot an enemy while another enemy is facing it then the ally of the killed enemy is still standing still not even panicking or making an alarm to give alert to his fellow soldiers. And lastly, they're insensitive even they're getting shot or their post is getting shot.
Second: Clearing the Path before Shooting
When a ranged unit is placed inside a building and an enemy is outside of it, make it look for a clear path to shoot at the enemy not just shooting the interior of the building then destroys it just to kill the enemy. Or make the ranged enemy go inside the building to kill the unit.
Third: Taking Cover and Protecting Themselves
Ranged units aren't taking cover; they're out in the field while in a gunfight but there are lots of covering places around them but they aren't taking cover specially when they're in a forest. And if they "think" that there is only one enemy alive (they only think that it is true) and they are many, they can go to the field because they would think they're safe.
Fourth: Being Concerned with Their Fellow Teammates
They're too insensitive to their teammates, they don't care whether their teammates are dead or not and like the Second one, they don't care what they hit like the obstacle, and sometimes they kill their own teammates because they're in front you should make them avoid shooting through allies and obstacles except when they have low accuracy. And please make them heal their teammates when they have medkits or first aid kits.
My suggestions are only here and it is not for me, it is for your game and for your players. I hope you understand everything I said. Thank you