The taper is for more volume, as is the bell. I personally find smallpipes a bit too much on the quiet side. Fine for solo indoor playing, but limiting when other instruments come into it. This slightly tapered variety has a bit more presence with other instruments, though it's hard to tell as generally it depends on the number and combination. For example, when I tried playing with a really loud hurdy-gurdy (of the Hungarian type loudness, though not of the actual type, these ones are very much louder tan the more familiar French types), well, I had to give up, as I couldn't hear the hurdy-gurdy . The pipe was very much like Luife's one, except different fingering. On the other hand, when playigng with a tabor pipe, it's just right.
By the way, Matthew, I haven't forgotten about your set, it's in the works. Sorted out the brass problem by now, so it's down to making all the wooden fittings for the drones.