I think we have discussed about it before, and AHOY had shown that he received something like $75+ for pre/post monthly bonus IIRC.
Other example is coming from myself, I used to get max $35 only no matter how much I lose and wager but there were few time when I received more than $50 after the change.
But as usual, every formula for bonuses at Stake will always remain a mystery and we will never know the exact formula how they count bonuses.
Ah ok at least we have another reference regarding this one, for @AHOYBRAUSE it might be understandable since his wager is $100k or more every month and you also said your wager is around $50k or more per month it's kind of over the wager target so you get extra bonus, me and most other users did not exceed the target so we got a fixed bonus. Yeah it's a bit hard to understand how they apply the formula to the bonuses while we can only guess. What is clear is that this information will be a reference in future discussions.
By the way, just wanna share that this month I got 2 birthday bonuses, 1 from VIP host and the other 1 through the official Stake's email.
Surprisingly the amount given by the VIP host is 2x bigger than the one I got from the email

I have no idea how can even it is possible although maybe the total amount was from Stake's promo funds but distributed in 2 ways.
But it will be more reasonable if the amount given through the official email is the one which bigger than the bonus given by VIP host
Another mystery thing at Stake related to how their bonuses works