The reason why I wrote that I have never heard of a brythonic use of 'ric' is because there are no actual examples, just extrapolations from old irish riagol from latin regula, rule. The germanic use is very well attested, whereas a brittonic examples are absent and suggested links tenuous.
The start of the legend on the Tancorix stone reads "Tancorix mulier.....". This is translated as "Tancorix, wife". There is no objection to the translation, but Tancorix looks to me like a male name and I wonder whether the stone attests the collapse of declension and case in Late British Latin and is meant to read "Tancorix's wife...". Makes no difference to the matter under discussion, but an interesting aside.