Griffinonwing, the calabash has a v-shaped cavity, where as the chimney has straight walls. Some claim shape affects the flavor but the opinions are wildly inconsistent.
Heres is something Greg Pease has to say on the issue:
Wider bowls tend to provide more flavor intensity, with the wood playing somewhat less of a role in the smoke. This makes perfect sense, of course. There’s more tobacco smoldering, and the surface area of the ember increases with the square of the chamber’s radius, while the amount of briar in contact with the ember increases only linearly. Taller bowls result in an increase of the “filtering” action of the tobacco, softening the taste in the beginning of the bowl, and gradually building up greater and greater intensity as the tobacco is consumed. Tapered bowls exhibit somewhat less of this tendency, though if not packed very carefully, they can become so moist at the bottom as to be difficult to keep lit. Shallow bowls seem to hold a purity of the tobacco’s taste longer, if not as intensely.
There seem to be limits, though. A full flavored tobacco in a very tall bowl can build up too much intensity toward the end of the smoke, and can become tiring, or even acrid if everything isn’t just right. Too wide a bowl can yield too much of a tobacco’s nicotine content, if it is high to start with, especially to someone sensitive to its effects.
http://glpease.com/BriarAndLeaf/?p=7