The bad news is that birds right at the camera are a challenge for any system (including my D6 and 600 F/4). The trouble is, a bird's head right at the camera is a tiny target - and the wings right behind the head look really good. Normally, Group AF is pretty good at that scenario, but not always. It also can depend on how far the bird is from the camera - basically, the smaller the head, the more likely the camera is going to go for the wings. If you're getting a lot of near-misses (like sharp wings, slightly soft heads), stopping down a bit can help sometimes.
Also, sometimes you need more shutter speed with the bird coming at you than when you're panning at the side. So, more shutter speed might be the answer too. I think Group AF or single point if you can keep it on the head are the right way to do (Dynamic can work too, but it may be prone to grabbing wings if they are a similar color to the head).
