I remember Koshka stating that Base Goku (Saiyan Beyond God) could actually be a hypothetical "pre-failure ritual SSj God Goku."
Remember when Goku and the others failed the first time because they didn't have enough Saiyans? Gohan implies that SSj Goku (All Powers Absorbed, a.k.a. failed ritual) "had an enormous Ki," implying that he was above everyone else. And Gohan sensed Enraged SSj2 Vegeta, so SSj Goku (All Powers Absorbed)>>>Enraged SSj2 Vegeta>>>everyone else. Basically, it's a REALLY big increase in power. So, it likely altered how SSj Godku performed against Beerus.
It's possible for the 50x multiplier to work if you assume that Goku's God-enhanced base form is going off of a hypothetical normal power Godku.
Basically, SSj God Goku (Post-failure ritual, a.k.a. the one who fights Beerus)>>>>>Base Goku (Saiyan Beyond God)>>>SSj God Goku (normal power, pre-failure ritual).