I've had that happen a lot as well. Sometimes it feels like they're not vision impaired at all.
I will say that they're better in .13 than any other version.
In a previous version they had instant lock, even when they had their back to you. Didn't matter whether or not you had cover, night time or anything else. They could see you.
I just tried the new map for the first time and I must admit that's the first time I've actually disliked the experience of ITR2. What a horrible horrible map.
It feels like they designed the map specifically to hinder your sight while boosting the enemie's.
They saw me form a mile away, behind dense foliage, trees and hard cover.
I do not believe a single enemy actually saw me. They all immediately began shooting in my direction through the foliage. It took them seconds to have eagle precision with their shots.
I just stood there... baffled... starring into the dense foliage that blocked my entire view of what was going on and it looked like something out of a Star Wars movie. I wish I had recorded it. Bullets where flying everywhere. From 180 degrees in front of me.
They kept yelling "Target in sight", as if they could actually see me, however, I assure you... They could not.
Right out the gate I dislike the map. If enemies where bound to the same rules as us I think the map would be super fun but as long the mimics have the super powers they have I think I'm only gonna go there for priority missions and even then... I just closed the game. I got completely turned off from the it. Holy crap.