Minnowbooster rates

It's possible I'm missing something, but recently my payments from the minnowbooster bot have been much lower than in the past. Initially, I attributed this to a low steem price, but after a little research, it doesn't seem to add up.

I lease about 28,000 SP to the minnowbooster bot

Screen Shot 2017-10-23 at 6.50.45 PM.png

I get paid about $5 - $10 per day

Screen Shot 2017-10-23 at 6.50.34 PM.png

If I start a contract for 4 weeks, I find that I can lease 28,000 SP for 746 STEEM or $24 SD/day.

Screen Shot 2017-10-23 at 6.55.44 PM.png

This means that the Minnowbooster bot is taking a profit of $14-$17 per day on the lease. Is my math correct? Can anyone tell me if I'm off here? I'm about to turn off my delegation but wanted to make sure I wasn't missing some key piece of information.