It's easy to install diffusion-screens (compared to lenticular rear-projection-screens), because the angle of infalling light will be the same for the outcoming light. This is both vertical and horizontal.

Projecting-screens is most installad vertical, either by hanging or fixing in a wall or totems.

To obtain the brigtest picture and best result, IT IS IMPORTANT the projector shoots toward the viewers. This will often implement the projector is hanging high, shooting down. It's not important, wich angle the light shoot to the screen, as long as the projector can keystone-correct for it.