Posting frequently can affect your curation rewards, but not your author rewards. Other people who have upvoted your post who then go on to upvote a lot will reduce their contribution to your author reward but changing the value so much with a minute to go and an increasing steem price? That doesn't make any sense. Unless the final calculation is only happening right before payout......but I'm fairly certain the reward values are more dynamic than that and update continually. I think this needs looking into.