Here is another observation that I did not expect. On the triangle patch in the center of the image, even though the edge nearest to the camera is nearly twice as long as the other two edges, all the edges appear to have the same tess factor! I know I can set them independently, so the three edges must be calculating to the same clip space length. That also explains why one edge is not lining up with its neighbor. It looks like my clip space calculations are wrong, because the distance between the edge points are always the same which is not the case.
Actually this consequence is visible in the above example as well. All of the edges of a single triangle have the same tess factor. What am I doing wrong?
EDIT: wrong again actually. Only the 1 and 2 edges are always the same, the 0 edge appears to be independent. I have no idea what's going on.