The amount going to Humble is the most, even the the Humble slider is the lowest.
Now you’ve got me wondering whether a client-side change would work to unlink the sliders and set them all independently. Could just be sending one value (the Humble slider’s position with the other two determined by splitting the remaining percentage) but if all three values are submitted and pass whatever validation takes place on the server, this could be fixable. No argument that it’s a shitty design though.
You could check your browser’s dev tools network tab and inspect the request. There isn’t much “hacking” you can do here though. If you send a low enough total amount, you just won’t get the games. If you send a higher total amount, you’ll get charged for it. This interface comes before the checkout proper.
It would still be interesting to get some insight on how this works though.