Technically, I get that Visibility as the Damage Prevention Channel would block radial damage, because the meshes of the actors are blocking the sphere trace.
However, I’ve set my Damage Prevention Channel as WorldStatic (which, to my understanding of the channel, should be things like the world object, unmovable walls, and so forth), and I’m still having the same issue as Jechli.
I worked around this issue by using a previously created custom collision channel that I had initially created for a camera boom. I set the Damage Prevention Channel to that and the radial damage worked fine, but this won’t allow for damage prevention by things like walls, floors, ceilings, or barricades without specifically setting each of those to that Collision Channel.