As an aside, in the Nova documentary episode "Rat Attack" (about how bamboo flowering leads to a rat plague that devours nearby crops and produces famine) (
link to video on YouTube), you can see how flat-ended dhas are used in planting fields in the Indian state of Mizoram by the Myanmar border. The pictures are scattered throughout the early video, but you can see it fairly clearly at the 19:40 mark.
They use the square ends of their dhas as digging sticks, and I'm willing to bet they don't have a distal taper on their blades either. The lack of a distal taper may be functional.
F