/3/ - 3DCG

What am I doing wrong here?

I've got a bone for each eyelid, placed so that the bone and the edge of the lid are lined up exactly from the side. The edge of each lid is set so the bone has 100% influence all along it.

In my mind, this should mean that when I rotate the bone around the x axis, the eyelid should follow it in a uniform manner. However, when I actually do it, the centre of the lid seems to move further than the rest.