How should a house shared vertically (ground floor and upper floor) be partitioned?

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If co-owners request partition of a house sharing the ground floor and upper floor, and one requests partitioning the ground floor and upper floor separately between them without harm, the other is compelled. This is because the structure on the land follows the land in sale and pre-emption. If one requests that the ground floor go to one and the upper floor to the other, to be decided by lot, the other is not compelled. This is due to three reasons: the upper floor follows the ground floor; they are analogous to two adjacent houses where one cannot demand that each house become a separate share; and the owner of the foundation owns the air space above it, meaning giving the ground floor a share would result in the other owner exclusively possessing the air space, which is an unjust partition.