Perhaps your 3 consecutive promotions before that meant that you couldn't go too much farther up in STH. Did you track STH? But perhaps you're right, there's probably also an effect of the previous season record.
I know that hte first full season I played, I made the finals and lost (2nd best record leaguewide). Had a ~400 STH boost. Next season I won the finals, and promoted (best league record overall). STH increased 500.
Then, when I joined the D3 I'm currently in, we had a team who lost in the finals 4 times. He had a big arena, and consistently filled it, even with strong pricing. Perhaps it's just the strong record overall?