Ofc. The post monthly or monthly bonus is calculated only according to the wager in the period.
I just wanted to clarify that there is no minimum, so it is not correct that you always get the same bonus when you wagered... the variable is the amount wagered.

That makes total sense if you look at it from the casino's POV. It makes more sense that you "reward" the active players or make it as attractive as possible. From dead accounts that only claim the bonuses, they have nothing... I'm surprised that you still get atleast something.
It surprises you because you think wrong, it doesn't make sense from the casino perspective as you say to reward the active customers and to not give anything to the dead ones, actually. Active customers don't need to get hooked, they are already here while those who left because they've lost too much money or because they've found a better place need to be attract there again. So even if you don't bet there since several months, you'll still get these bonuses.