I believe the scan doesn't see them through walls unless they're stationary. It seems to pick them up through smoke even when they're moving. I'd say it's also situational, but lots of things are. It's really funny to silenced-KSG someone through a cloud when their outline is staring right at you, completely oblivious.
I really don't like it because of the constant wave that the sight does. It makes me lose my enemies in the sight a lot of the times. I might try running PDW MMS Stock and Silencer with Scavenger and Smoke Grenades.
There is no pleasure in life. There is only a relief of pain. We have to suffer to be on top.