.. on Howard's FAQ site makes me wonder if I have a Tin Chirra UBE. Sanu went his own way on my 19.5" (it was his design, and he's still working on it), and I only lately discovered that the edge bevel is fullered. Although it is shallower than the other two, it is very evenly done, and runs the length of the edge. The smaller UBE has a flat edge bevel.
The smaller has the carved handle, and the big one has the great piece of burl, so there is no way I'd mess with that, just to find out, but I believe the larger knife may not weigh any more than the smaller one, given the thinner spine and the fullers. The burl is very likely the biggest part of the weight difference.