Maybe the effect of pairing favoritism is that, if two stories are equally good, the reader will have a warmer emotional connection to the one that has, e.g., Sam/Dean rather than another pairing, or that has McDex and not Ronon with Zelenka? (Ceteris paribus means "all things being equal" btw.)
Ceteris Pairingbus
(Ceteris paribus means "all things being equal" btw.)