To what extent are the radius ratio rules valid for predicting the crystal structure of an ionic compound?

The ionic radii of $\ce{Ba^2+}$ and $\ce{O^2-}$ in barium oxide are $\pu{135pm}$ and $\pu{140pm}$, respectively. The ratio of the radius of $\ce{Ba^2+}$ to $\ce{O^2-}$ is approximately $0.964$.


According to the [radius ratio rules](https://en.wikipedia.org/wiki/Cation-anion_radius_ratio) the solid barium oxide should crystallise in a body-centered cubic type structure (like $\ce{CsCl}$).


[![Radius Ratio](https://i.stack.imgur.com/iweeM.jpg)](https://i.stack.imgur.com/iweeM.jpg)


But [evidently](https://www.webelements.com/compounds/barium/barium_oxide.html) the prototype structure is $\ce{NaCl}$ type.


What is the reason for this anomaly from general trend?


EDIT: I found that every alkaline earth metal oxides (Of the type $\ce{M\_{alk.e}O}$) possesses rock salt (halite) structure but only $\ce{MgO}$ obeys the radius ratio rule (it has a radius ratio of about $0.64$ which is well between $0.414$ and $0.732$).


Certainly as we are going down the group the cationic radius is going to increase and so is the radius ratio.


