Bear in mind that the sketch is exaggerated for effect. Jarrod talks about honing a surface like a 20' wide basketball. If you translate that (10' diameter) to a 6" long stone, then place a straight edge on the center of the stone... there will be a gap of 0.037" (0.95mm or just over 1/32") at each end. Pretty tiny.The picture above is odd to me relative what i thought i saw. It supposes that the ark will wear the bevel side where it meets the blade face away when honing. Is an ark face enough to cut that steel? (reminds me of honing a near wedge and how much of the bevel face wears away before you get near the edge.)
Again, the sketch is exaggerated. If it was drawn to scale, 0.037" is thinner than a pencil line.
So, setting the bevel on a flat stone and finishing the edge on a convex one is no doubt quite doable.