The thing about mother nature and the laws of physics is they apply to all with out bias.

Consider a 5G tube / pipe but weld (clock positions approx)

On the vertical down side from 12 to 3 the pool want to drop into the ID

After 3 to about 5 the pool is pulled down you tend to get less ID reinforcement

From 5 to 8 the molten pool naturally wants to drop to the floor

After 8/9 to top dead center the pool want to again drop to the ID of the tube/pipe

Of course gravity has an effect in welds. For example, all covered (stick) electrodes are suitable for plane welding, when gravity helps the melted metal to drop into the joint, but not all electrodes are suitable for overhead welding, in which gravity works in the opposite way. Similarly, most electrodes are suitable for vertical up welding, when gravity works in your favor,
but not all of them are also suitable for vertical down welding, when gravity is against.
Giovanni S. Crisi
Sao Paulo - Brazil