And maybe I was point-scoring by pointing out that claims of being 'natural' are really rather shaky.

However the bees do prefer vertical rather than horizontal. If you give your 6 active frame brood box early spring colony three supers of foundation now you would find that they would instantly stop spreading outwards and move up instead to create a chimney of brood and stores up the middle. It makes sense to get them to fill their brood box first, and so there is a narrow period for the ideal timing of adding the first super as they approach the edge of the brood box but before they feel cramped.

Maybe in warmer places the tendency to work upwards is less?

best wishes

Gavin