Hello, currently the code does not prohibit a maximum amount. However, you should look at the expected upvote payout based on the bots current Steem Power. You probably see the best payouts when bidding is low for a round and you bid at least 0.1 SBD to receive additional votes. Remember, no payout amount is guaranteed and it fluctuates with the price of STEEM as well as the amount of competition for bids. Thank you