when is 'flat head' too flat?

[theotherhand]

My DS has a flat head. A patch of flatness, I suppose, more accurately. He's 16 weeks. When do I worry and think I should do something about it? We do a fair bit of tummy time but obviously he's mostly asleep, on his back, at this age...

Don't want to worry but do.

Take him and get his assymetry measured. Try tummy time. Look at yahoo sites on plagiocephaly. Lots if threads on it on here too.