according to UE docs (pasted below), seems that what you want to detect influences ‘by channel’ or ‘for objects’. i setup a custom channel in project settings, then did line trace by channel to detect hits on only the elements i am interested in.
"Channels are used for things like visibility and the camera, and almost exclusively have to do with tracing. Object Types are the physics types of Actors with collision in your scene, such as Pawns, Vehicles, Destructible Actors, and so on. "
"Multi Trace For Objects will return everything that matches an object type the trace is looking for, assuming the component is set to return trace queries. This makes it great for counting the number of objects between the start and end of the trace. "