That's correct, the amount of curation rewards depends on your Steem Power holding. But it also depends on your work ethic, skill and understanding of the rewards system. For example, I make more in curation rewards with 50,000 SP than most whales with 1 million SP. When I was a minnow, I still made pretty decent rewards. The key is to find undiscovered posts and try to get the word out about them. Voting on trending posts is a sure fire way to never succeed at curation rewards.