Ditto
Harold Vaughn, in his book Rifle Accuracy Facts, describes having experimented with every crown form from square to taper to the traditional sporter's toroidal section. He feels he proved to his own satisfaction that it made no difference at all, provided the crown is symetrical about the bore axis.
Some, like the square crown, are easier to cut. Vaughn declared the origin of the popular 11 degree benchrest crown a mystery. He thinks a benchrester confused the fact 11 degrees is the maximum angle a subsonic boattail can have without creating extra drag with somehow positively affecting the muzzle gas jet's impact on an exiting bullet. It doesn't. It might as well be 10 degrees or 14 or 30 or 7. Just keep it axisymmetric.
Nick