Tapering TL-speaker, why?

[MJ Dijkstra]

I have spent many hours on the web to gather information about TL's. Regarding tapering I have read different opinions.
Some say the taper will reduce the standing waves within the enclosure. That's obvious but I think you could get the same result by making the walls nonparallel as with a circular tube.
Some say a tapered line can be made more compact. Some say it effects the width of resonance. So......

1) could I make a decent TL without taper? (most commercial ones are tapered.....)
2) Does a strong taper make the TL sound more like a closed box?

I've got rather small units of 13 cm so the size of the TL will be moderate, tapered or not.

Thanks!