Surface finish in a scintillator crystal using Unified model

I have a scintillator detector wrapped with teflon .I am interested in using Unified model . I want to change the reflection components like specularlobe, specularspike and backscatter to get the desired result.
I am not sure what interface I must used dielectric_metal or dielectric_dielectric ? Also what Finish I must set ?

Here is the code

   G4double reflectivity[2] = {0.95,0.95};
   G4double specularlobe[2] = {0.0,0.0};
   G4double specularspike[2] = {1.0,1.0};
   G4double backscatter[2] ={0.0,0.0};

Have a look at the diagram and see if that answers your questions.