We don't know if the taper does anything though. If we don't have a working theory we can't really use variations of the working device to prove anything.
Oh I had thought that the asymmetric shape with the tapered cone shape was an important feature from the original inventor. But yea, hard to guess without more systematic theory to leverage off of yea..
From what I've read, the theory amounts to "there are more photons bouncing off the fat end versus the thin end hence thrust." Which personally I think is highly questionable given the low-energy regime involved.