In summary, the structural arrangement of Bi atoms into a pyrochlore network of Bi tetrahedra intercalated with alkali metal atoms, results in a relatively high electron-phonon coupling constant. This emerges as a combination of both aforementioned factors: the large electronic density within the closepacked Bi atoms in Bi4 tetrahedra allows for the strong interaction of phonon modes with electrons (large phonon linewidths), whereas the tetrahedra themselves are relatively loosely packed within the unit cell with a large amount of "free space" filled only by Rb/Cs atoms. This, in combination with high atomic mass of Bi, results in relatively low Bi phonon frequencies, enhancing the EPC. Recently we discussed a similar situation in isostructural Laves phase superconductors: SrRh2 and SrIr2, where the pyrochlore lattice or Rh/Ir was found to be responsible for the emergence of strong-coupling superconductivity.