Variations of the size of the rings of bimetallic coins

I think something like this is not a variant:
https://en.numista.com/catalogue/pieces6528.html


the difference is only the position of the different metals.

You are right. That's not a variety, that's just an error of the planchet. Inner ring of any bimetallic coin can sometimes move away from the central position, i.e. closer to the border.