We notice that when the nucleus becomes smaller with respect to the electron cloud and thus as the value l/d becomes smaller this also results in a smaller effect of the quadrupole term.
We notice for example that the difference between the energy contributions of the theta = 90 and theta = 180 for the l/d = 0.60 case is around 0.5 while this same difference is only a meager 0.012 for the l/d = 0.05 case.