The rewards are only reduced for accounts that don't do at least a little gambling, buying lottery tickets or deposit to keep a higher balance.
Whatever move you do, those botnets will keep adapting and finding ways to drain the faucet. I think the only thing you can do is lower the base reward even more for such accounts so that it isn't profitable anymore.
I suppose the problem here is that not all such accounts are bots. I wouldn't be surprised if most of them aren't.