Why are 2nd and 3rd ionisation enthalpies of Bismuth more than that of Antimony?

There is a very small increase in size from Sb to Bi due to completely filled f- orbitals in Bi. As we know that after removing one electron the size of cation further decreases. This decrease is higher for Bi as compare antimony. So, in case of Bi it needs more energy to remove 2nd and 3rd electron from cation. Therefore higher 2nd and 3rd ionization energies for Bi.