In theory capping it sounds like a good idea, until you realize how many really small bets are being placed that are going to win. 50% sounds reasonable, but making it a percentage will make it last forever. Maybe make it 50% or X clams, whichever is greater, or the Bot balance . X could be any amount. IE 5 clams. I'm rambling so...
If X is 2 clams and the balance is 10 clams Max payout would be 5 clams (50% rule)
if the balance is 3 clams, Max payout would be 2 clams ( X clam min rule)
and if the balance is 1.9 clams Max payout would be 1.9 clams (balance rule).
Bots don't always win. And it won't really last 'forever'. With 50% it can still easily lose a big majority of its balance. And since there are so many rounds its quite likely. What you want is a bot where the balance will last for awhile so you don't need someone to keep tipping it. The balance can easily disappear with 50%. And implementing the X rule on 50% just makes the balance disappear faster.