I think it's more of a mapping thing. In the lower right is the actual UV map, I've just coloured it so you can see better how it falls on the mesh. The lavender  part on the UV map is noticeably thinner than the pink part, yet on the mesh covers almost the same space. You can see the stretching on the lower part of the lavender strip on the upper eyelid. It's really not that apparent unless you do closeups or there is a contrasting colour such as makeup.