I have the same problem. Hell, my tank will even go to the edge of my set radius just to avoid pulling the mob right next to the group. It can happen to me in any zone so far. No matter how I adjust the settings, it doesn't fix it. I have seen cases where I can move him over 10 feet and restart the mac and he magically sees better, even when there are no elevation changes. In GD at the Laima camp, no matter where I move him in the room, he never sees more than 2-3 mobs. I tried for hours to move all over the room and no luck. Gave up and now I'm only getting 3 mobs that happen to be PH. Sigh.