In addition to the obvious wireframes (which, now that I think about it, aren't exactly helpful here) I've included an alt upper left image. Same pose and so forth as the Shape Review's equivalent, except this one has the alt color thin eyeliner and my bog-standard lighting setup.

As for the wireframes, you can (barely) see that the changes induce an additional edgeloop along the lower eyelid. This accomodates the smooth interface between the upper and lower eyelids. What is less apparent, is the addition of an edgeloop on the thin border edge that separates the inner part of the eyelid from the outer. This, combined with the other edgeloop was the key to getting the overlapping shape.
You can picture it as two flat tires rendered as toruses (torusi?) stacked next to each other, the top of the one in back has been cut off, but its base has been pulled out underneath the tire in front, whose base melts into the base of the cut one. Or something like that.

The result is a magnificent improvement in looking like the real shape of an eye with surprisingly good deformation.