... at the same time, however, there is little space on one's own towel, so "downwards" is not completely stupid. But I still consider the fear to be unfounded. If a developer builds both halves, they will make them the same anyway, and if there are really two separate, completely unknown developers, it will be very expensive for the basement builder (their bad luck). But you know that beforehand, so there is no need to fear bad blood.