FUR'd.
Looks like somebody has perfected this science although as you said Post Rewards are the sum total of those upvotes by bots and nonbots. Author must have good quality posts I presume as I don't think bots can give you more than 2 or 3 times the investment. Or can they?
The bots are giving back negative returns lately (less than double) , so it ends up costing , but because the post gets on the trending list, people hammer with upvotes to get the curation.