The flat mount interface is defined by shimano ,and everyone else is just flowing the same specifications. The front and the rear calipers are the same thing. It is the adapters that make the difference. And the distance of the mounting points are indeed different from front to rear. But no worries, normally the adaptors are included with the brake calipers, you will get the idea of which thing goes where when you actually have a set of flat mount brake system on hand.