I think I have a roll of that tape, if you can design a experiment I can try it up to 300Mhz
putting a sheet between a signal and receiver coil (like NFC coils?) might work as a test?
I thought about it because of ferrite rod antennas, big ones, where you have the option of using ribbon cable as a shield, but I still am not fully sure how ferrite material around the coil acts like, so its possible to make a rib-cage of magnetic tape to experiment with ferrite rod antenna characteristics, if it has a different from solid conductor metal strip material, or to find out if sticking it on top of strip material might do something desirable
Something tells me a proper test is laying it on the inside of a horn antenna or TEM cell or something (waveguide?) maybe, to see how much signal gets out? My horns all have polarization layers or optics on them though