best for spark transfer; dull or sharp edges?

Someone explain a Nippondenso U-groove then. I dont think they did all that R&D on a dud design? Modern plugs are very small tipped. I think its because the platinum/iridium/ruthium is so much better at not corroding/burning off it can be made very small (plus its expensive) while the Champion pencil lead tip had to be made fatter to last longer. Interesting topic, need some links to some white papers on the subject.