With a smaller nuclear size, the quadrupole interaction plays a lesser role because the charge distribution can be more accurately approximated as a point charge. However, in the three graphs, the quadrupole term appears equally distant from E0, which is a result of the vertical axis scaling. By comparing the vertical axes, you can see that at 0.6 l/d, the scale differs significantly from that at 0.05 l/d. This difference demonstrates that at 0.05 l/d, the quadrupole contribution is indeed much smaller.