The beam tool doesn't have cover fills. Why? I don't know. I hardly use the beam tool because of it and instead use anything else to draw beams with. I think I used beams once for cutting holes, but otherwise it's usefulness is hampered by not being able to apply cover fills. Maybe someone can give a reason why to use beams (maybe for complex profile solutions) but I haven't needed them.
btw, there are beams in the object library that have cover fills. I use when I need actual beams.
