This is what my current test rig looks like:

I use two identical cube meshes out of Blender at subdivision level 1. One is unmorphed, the second one has three morphs M1, M2 and M3 with constant deltas in the first, second and third coordinate direction, respectively, for all the level 1 vertices. I'll call those directions n (for normal), u, and v, respectively. The base level vertices stay where they are.

It seems that for each level 1 vertex, either u or v follows one of the edge directions adjacent to that vertex. So far, though, I haven't figured out when u and when v is chosen, and which of the edges is used. The next step could be to export the morphed results and run a script on them that relates the displacement to the OBJ data in order to see if there's some discernable pattern (e.g. always move along the first/last edge the vertex appears in).

-- I'm not mad at you, just Westphalian.