I have no idea what the algorithm is, but I do know most of my curation rewards have been a fraction of a cent. I guess it adds up after a while, but you'd make more money leaving ten comments on people's posts than by upvoting 100. I'm not saying don't waste your time upvoting. Just, don't waste your time upvoting for the curation rewards. Upvote the content you like because you want to reward good content creators. Then leave a comment on every post you upvote.