If there are surfaces between the members in the area load plane (wall or roof surfaces) that are not displayed in the model, you should use the "Fully closed plane" option. Thus, the surface load affecting the entire plane is converted to members.
However, if the structure consists of members only, for example in the case of a lattice tower or a truss girder, you should select the "Empty, on members only" option. Thus, the load is applied to the effective or projected surface that is composed of member cross‑sections as a load area. In this case, the load is applied with regard to the member position.