Hi,
Let's talk about a ground plane:
I have a "problem" in thinking about how "return current" will flow. In any signal integrity & EMC book / advice one can find the statement that "RF current will flow back on a GND plane directly under the signal line". That is why you try to minimize the "current-loop", avoid plane splits, ...
Obviously they are talking about the maximum of current density in the return path. Maximum current density will occure on the path where minimal resistance exists (for the particular frequency).