Leaky Coax Modeling Issue

I am attempting to model a short section of leaky coax with a single slit in the center of the outer conductor with FEKO Suite 7.0. The model is attached. We are trying to evaluate the S₂₁ value between two waveguide ports on the ends of the cable segment but the resulting S₂₁ value is essentially zero (about -115 dB), which I believe is incorrect. When I replace the lossless user-defined dielectric medium of 'ePTFE' with free space in the dielectric of the cable, the S₂₁ value becomes more realistic (about 0.995). I believe there is some mistake in my modeling of the dielectric between the inner and outer conductors.

What restrictions are there on modeling dielectric materials, specifically regarding the assignment of dielectric materials to regions and faces? For instance, in modeling metallic objects only the faces are assigned the desired metallic media of the modeled objects while the regions are set to free space; I do not seem to be able to set the faces of the dielectric to the desired dielectric media (while I can set the 'Jacket' and 'Dielectric' regions to the desired dielectric material) and assume the same rule does not apply to the modeling of dielectrics. What are the 'Default', 'Dielectric Boundary', and PEC face media specifications used for in modeling dielectrics?

Unable to find an attachment - read this blog