Whatever it is, it certainly cannot be more complicated then the provably fair games themselves
I am quite confident that yes, it is more complicated since it's individually calculated. Provably fair is just provably fair across everything, for everyone. One user won't have a more provably fair hash than any other user whereas someone's gambling habits will differ A LOT between all users.
Besides that, just showcasing exactly how they'd calculate rewards would never be a good idea since casinos operate on a customer retention basis and giving your competitors fuel to take those customers from you would basically be suicide.
You make a good point there about customer retention.
Even if they dont disclose full formula its in their interest of 'fairness,transparency' points these casino advertise themselves on , to atleast give some sort of standardised calculator so people dont feel like they getting the short stick