Well, I can quite imagine that the air exchange is better ensured if the supply air in the room above is extracted diagonally through the door gap into the room below. Whereas the supply air from the floor outlet is only extracted again at the floor through the door gap, so it cannot exchange the air in the entire room! Or is there more to consider? Or other advantages/disadvantages?
There is much more to consider...especially floor air outlets are a great example...completely different airflows can be set just by changing the angle of the louvers...
So we were at various model homes over the weekend and there was really everything. From ugly decentralized huge boxes to really discreetly beautiful central systems in the walls and in the last house we even saw some in the floor.
gurgle up: l03301d_dimensionierung.pdf those are the grids which I, for example, use with us, it is explained quite understandably how the air distribution changes when you vary the size and the different slats.