[mikelessard]

Before. I'd get it as close to the antenna as possible. If you're up for getting on the roof (and it's safe) I would buy the shortest pre-made RG6 cable I could get, attach one end to the antenna, the other to the "In" of the filter, then the existing cable to the filter "Out". Don't take any unreasonable risks though, it's not worth it. As long as it's inline between the antenna and the TV it will help.

I don't have your plot so I don't know how close to the mountain you are. I wouldn't be shocked if you needed 2 filters to get it all. In my situation with The River (97.1) my preamp has a built in FM trap, but it wasn't enough. I still had to add the 2nd trap. It is exactly 5.0 miles from our site.