Just a thought, but in recent times, the shape of the core seem to have much less to do with the ball's reaction than it used to. I've seen plenty of tall, "thin" cored balls have a smooth reaction, plus I've seen plenty of round-ish cored balls have a flippy reaction.
While the standard still holds, "70% of a ball's reaction is determined by the coverstock/surface", other than the bowler,'s portion of the "blame" for the ball's reaction, a ball always equals cover + core. Besides that, one can always influence the ball's designed-in reaction by using drillings, including pin-PAP distances, VAL angle and Drilling angle, as well as the surface preparation.
So, in summary, I'd worry more about the basic design of the ball + your own style of bowling much more than I'd worry about the shape of the core.