I just finished episode 299 and have a (probably wrong) solution to the sort issue. Can anybody give me an example of where this wouldn't work?

If both entities are horisontal sort in Z.
If both are vertical sort in Y (using the entities smallest Y).
If one is horisontal and the other is vertical sort in Z (using the vertical entitys top Z).

That is actually the sort criteria we end up deciding to try, assuming I'm interpreting your list correctly. But we then prove it's not a total ordering, so we're going to have to use something other than a total ordering sort in order to use it - and that's where we left off before my headphones broke :)

- Casey