Epoxy coating with fixed reflectance and refractive index

Geometry, Fields and Transportation
1

Hi everyone, my apologies for the very simple question. I am trying to make a scintillator detector rod, with an epoxy coating surrounding it. The epoxy coating should have a reflectance of 90%. The confusion arises because the refractive index is about 1.6, and I understand that the reflectance is computed as R=(n1-n2)/(n1+n2) squared. So I don’t understand how the reflectance can be that high since the scintillator itself will have a reflectance of 1.62…

    double Epoxy_RIND_2[E_NUMENTRIES];
    for(int i=0; i<E_NUMENTRIES; i++)
    {
       Epoxy_RIND[i] = 1.59;
    }
    double reflectivity_epoxy_glue[E_NUMENTRIES];
    for(int i=0; i<E_NUMENTRIES; i++){
        reflectivity_epoxy_glue[i] = 1.; // absorption length in vacuum...
    }
    G4MaterialPropertiesTable *Epoxy_glue_mt = new G4MaterialPropertiesTable();
    Epoxy_glue_mt->AddProperty("RINDEX", Energy, Epoxy_RIND, E_NUMENTRIES);
    Epoxy_glue_mt->AddProperty("ABSLENGTH", Energy, Epoxy_ABS, E_NUMENTRIES);
    Epoxy_glue_mt->AddProperty("REFLECTIVITY", Energy, reflectivity_epoxy_glue, E_NUMENTRIES);
    EpoxyGlue->SetMaterialPropertiesTable(Epoxy_glue_mt);

I have tried setting them individually but they are not really working as intended. Can you please help me and, if possible, suggest a way to circumvent it?
Thanks,
Simone