why an interstitial defect increases density in covalent solids and do not increases in ionic solid?

The interstitial point defect increases the density of a solid. Frenkel defect is also a type of this defect but it do not increases the density.


Also, the mass / volume concept of density tells us that density should be same in both cases, as they are basically interstitial defect. Then what happened to a covalent solid that density increased , and why it didn't happened to ionic solid?


(Please understand that it is not a duplicate of
[Why Frenkel defect does not impact the density of the solid?](https://chemistry.stackexchange.com/q/125400/121235) )


