If you dont use Stake much anymore, it is reasonable to see that your pre or post monthly bonus is getting lower than before. I've experienced it sometime ago. I used to get $25 from the post or pre monthly bonus but there were few times when I get less than $20. It means that our wagering activity will also affect this bonus so if we do wager regularly, we will get the same amount all the time but if we do wager less, the bonus will be less.