I doubt a thin film would eliminate the attenuation. If the problem occurs because the two antennas are electrically coupled, separating two conductive surfaces

I doubt a thin film would eliminate the attenuation. If the problem occurs because the two antennas are electrically coupled, separating two conductive surfaces by a thin film simply forms a capacitor that will still couple the RF signals in the primary antenna to the secondary. The duct tape hack and the bumper help because they distance your finger from the conductors.