The step down at the edge is to increase the preload the pressure plate. It's really up to your pressure plate manufacturers recommendation whether the flywheel should be stepped or not. If you need one and don't have it, the clamping force is reduced. If you have one and don't need it, the TOB and lever might be in the wrong position. I've never seen one like that, but then again I don't play with aftermarket KA stuff. The SR stuff is flat.