After lapping the fine and ultra-fine stones on the 400 grit diamond plate, their finish is definitely still different. I can also see the difference with my high power microscope.

The little scrap of paper information sheet that came with them said they're made from high alumina ceramic, formed when alumina particles (synthetic sapphires) are mixed with a ceramic bonding agent, then fired to make the final shape. I'd think it is the size of those alumina particles that are determining the grit of the fired ceramic.

As for the flatness, it is the flatness across the stone that I was after, not so much the flatness from end to end.

Before I lapped them, both the fine and ultra fine had clear high spots that were the only places on the hone that were removing metal from the edge. This was evident by the dark black lines that showed those high spots.

Now, they get a uniform grey from the removed steel, showing no high spots. I think this is the main reason the feel is so different. The full blade edge is in contact with the full face of the stone over the entire stroke. This polished the edge much, much faster than the unlapped hones. I'm thinking this must be because of the more constant contact with the hone.

But, the proof will be in the shave tomorrow morning. I gave it fifty laps on the linen side of my Illinois Strop Company 127 strop, and another fifty on the leather side this evening. Beard hairs only grow so fast...