How do the ionic radii vary within?
Well, we can answer this question.
A metal is an electron rich material, that commonly forms CATIONS....and we can represent this by the oxidation reaction..
The cationic radius is certainly markedly reduced with respect to the atomic radius. This is especially true for the alkali metals, which, upon oxidation, effectively lose the electron whose orbit constitutes the valence shell.....see here.
On the other hand, the anionic radius, involves addition of an electron to the valence shell of the non-metal. The atoms of the halogen group have markedly smaller radii than their halides ions.......
So the change in ionic radius depends on whether oxidation or reduction has taken place, in other words, whether we deal with a metal or a non-metal.