I mean that sense of relate which we find in:
A relates to B as C does to D.
or when we speak of A and B's relation, meaning whatever may be said of A and B without further specification.
If forced to give a definition, I would say that A's relation to B is how A stands to B, which is a metaphor (is it?) and couldn't possibly tell someone who didn't already know what a relation was.
Referō does not seem to have this sense.