I don't think I have ever see a MCA rating of 13.5 amps and an OCPD of 30.
In your example #14 would suffice for the MCA,,,,,,,but could not be put on a 30 amp breaker, therefore, #12 would be needed.
I disagree, NEC says to use the manafactures nameplate for MCA and MOCP, if the MCA
is #14 wire and the Maxocp is 30a, #12 wire is not required.