I use classical formulas for coefficients of reflection and transition (refraction) for both kinds of vertical and horizontal polarization for various numbers of permittivity, and permeability (see my books published in Wiley and Sons in 2007 and 2014). Moreover, we need every time for each type of polarization to calculate impedance, and for this we need also knowledge of conductivity of the material. What you have received - for zero and non-zero permittivity is not correct since you use only its real part and ignoring imaginary part, which never equals zero.

Many thanks for your answer.

Presumably for the e=0 case this is lossless, and the reflected wave from the front and back of the breakwater cancel completely, either by design or chance, when they have the correct phase difference. I presume that e is porosity, which introduces absorption of energy and a smaller reflection so that the two reflected waves no longer cancel because they are not the same size.