Maybe just up the militia's skill?
I tried that. But even at max skill level, I could be less than 50m away from them and still sprint right infront of them undetected
Instead, I would recommend using some alarm scripts or something like that. If the player wants to blast away then more units will arrive, and even if they can't see good they can see and they are many.
I don't really want to use an alarm script since it would seem wierd if a siren went of in the middle of a city. But, now that you mention it, it would be cool if someone jumped into a jeep and drove off to alert more people. And if you shot him in time, no reinforcements would come.
Whats really frustraiting is that nothing helps the AI to see in the dark other than NVG's. I agree that it's annoying when the enemy can stop you from 500m away. But, this mission is set in a city. And the fact that there are lights everywhere and that buildings restrict the AI's view, makes things really annoying. I managed to get withing 50m of a group of militia and sneek up right behind then and they didn't notice a thing.
In this mission, I don't what the player to focus on stealth. I wan't the player to go in guns blazing, machine gunners emerging out of ally ways to provide support, and snipers providing cover from the rooftops.