So Jack, I hope you've noticed what I meant. This mostly can be felt when you are alone among the enemies, because if there are friendly AI around you, enemy does not pay the same attention to you the more that you are behind cover.
I don't know what is the mechanism responsible for their behavior, but with my humble playing experience

I can say that it is kinda weird at the current moment the more that you say there are no recent changes. BTW Now I remember that something similar has happened before, but not for a long time.
Jack, you told us what the SAS settings are, but please explain us how and whether can be adjusted the behavior of the enemy. It depends on what?
EDITAnother example of tonight: battle of the bridge while trying to conquer Village, you wont believe - brown and gray are fighting shoulder to shoulder against us and another part of gray are coming from behind........