In doing some research and viewing other conversations and experimental tests among historians there are two answers, the official answer being that "no one really knows", and the answer that rises to the top of the speculation and especially the results of experimentation is that these arrowheads were for small ground game, rabbits and such. The rope cutting thing, rubbish, in experiments they rarely even hit the rope edge on let alone cut it. The horse thing, again rubbish, most experiments done on that kind of hide either with fleshy or boney backing the two prongs stuck in and that's about it. With birds they didn't do much to cut feathers in flight or that sort of thing and did more damage to the bird on direct strikes than one would desire, blunts are a much better, and well documented mind, option for birds. Smallish ground game though seemed quite susceptible to this type of point as not too much damage done, the width made for larger chance of hitting, and the shape acted like a judo tip in that it would flip the arrow or prevent loss in brush. Again, no one really knows for sure, but that's where I'd lay my money...
