it has to do with the strength of the steem crypto coin, it is a random variable as market movements are ambiguous to say the least. it seems to be that the coin is getting stronger, so again that is just my guess. as the price moves up and down every day.
money adds up even if it is little by little. as you should know that SBD is not the same amount of "value" as USD or Steem. their values fluctuate, so it depends on the market's opinion so to say on what amount he will have to make a day.

so to sum things up.
currencies, their value fluctuates dependent on the market value at the time, since i am not sure what the price will be from one week to the next it would be difficult to give too exact an answer on how much he would need to make

i hope this helps and would be glad to further explain my reasoning. i get distracted when i write a lot so i can clarify on what is not understood at the best of my ability, it is really just my guess based on some "broad paintstrokes" so to say, if that makes sense.

i thank you for your time and i hope that you have a good one.