It's to counted your previous weeks wagering with the current weeks, that's how we can make sure. If just by feels, it's hard to be track because they already have the system it self. If not wrong, we will have a new system.
The more you lost, you gain more amount.
Afaik the new system has been implemented since last week because my weekly is like doubled than what I used to get although my wager remains the same in average.
I lost some money last week and I received more amount than usual, that's why I think the new system is already activated.
Tracking our wager amount as well as our overall profit during a week is the best thing to do if we want to get better "guess" about how to calculate the weekly bonus.