I figured out how stalker 2 handles stealth

Because of two ways I managed to do stealth i figured out why a lot of people can't stealth.

This doesn't explain why they agro right at you no matter the distance or cover but it does explain why they agro to begin with.

First off, Line of Sight.

This means of you are behind an enemy, they won't notice you. Duh.

But if you kill an enemy infront of them, they will see it and agro to you.

But if you shoot the enemy behind them first, they won't notice.

If the ai can see a dead friendly they know where you are

Headshots. You need to down the npc so fast. Automatic fire and a supressor wont cut it. You need to make the first shot a headshot else they will hear the friendly npc cal for backup even if you kill them before they actually get anything out. A single supressed headshot on an enemy no one can see in their vision cone will not alert the squad.

Npc vision cones seem to extend to the same range the player can see them fade in. This means if you can see them. They can see you. There vision also ignores all tarain types and obstacles. If they are looking in your direction no matter what they are liable to spot you. Sometimes through walls when the whole area is agro but when not agro this means you can hide behind walls and trees but not grass and shrubs. If it doesn't have a hitbox then they can see through it.

So with all this in mind you wanna stay out of sight of the guys in the sniper towers. Headshot them before they realize you are there. Then you can pick off targets that either are alone or not visible to there friends. Like behind a wall. Kill him then the guy he was watching and chain it until you have wiped the area.

Also beware of your movement speed. You make noise and they have a hearing range. Crouch and move slowly.

Im sure this wont solve all your stealth issues as the AI can just ignore walls if your running around or they spotted a dead friend while patrolling. This is also why you can carry bodies. You can kill someone. Then get there bodys out of sight.

Hope this helps you when you attempt to stealth through any particular area.