Is there a justification for why are the $4f$ electrons strongly localized about the nucleus in rare-earth atoms but the $3d$ electrons in transition metals extend further out from the nucleus? I have hit upon this question while reading about magnetism. Here is a reference from Blundell's Magnetism in Condensed Matter Sec.4.2.2 second paragraph.
A slightly different quote can be found in Kittel's Solid State Physics book which says,
The difference in the behaviour of the rare earth and the iron group salts is that the $4f$ shell responsible for paramagnetism in the rare earth ions lies deep inside the ions, within the $5s$ and $5p$ shells, whereas the iron group ions in the $3d$ shell responsible for paramagnetism is the outermost shell.