Wager, deposit and rank all count while they send post monthly bonuses to member sometime its have good worth and sometime as normal as you already mention you have done no good wagering but still you have good amount I have talked to my friend who is doing good wagering, and he received almost nearly $100 as he is also Platinum member and I have never been above $5 as I am also not doing good wagering with my rank is also not good, but usually I am doing stuff regularly which is helping me something for having something from this and few more sites on monthly basis.
We are talking about pre/post monthly bonus here, I'm curious about your friend's account rank and how much he wagered that made him received nearly $100 on pre/post monthly bonus. As long as I know post monthly bonus is mostly based on VIP level only (fixed amount) but of course there is also requirement to receive the base fixed amount for the pre/post monthly bonus. I have never heard someone received nearly $100 for pre/post monthly bonus, at least no one who shared something like that in this thread. I know some friends who are between Platinum 4-6, their pre/post monthly bonus is no more than $50. Seems that you are talking about monthly bonus instead of pre/post monthly bonus.