HI Burr, also I don't really understand what you mean by this part:

"(to get both top edges of the parted model to display as "Z = 0")"

How is it that you're expecting the z size to be 0 units? You seem to have the full block at 19 units tall, so shouldn't you have each half block to show a z size of 9.5 units, exactly as shown above?

- Michael