Sarang, Ian pointed out the major reason why subs, for the most part, don't make use of non-parallel sides for the enclosure.
Hey, I explained it first. Ian just didn't use the Bran Muffin analogy. I guess I lost points for not being staff or not being the slightest bit eloquent.
Ian is, admittedly, much more knowledgeable than I and he has Shania Twain's Summer Home on the other side of his lake. I can't compete with that. I humbly concede.