It's a tough one for me to say too in depth without having been there watching at the time. A huge factor in the last couple of months was the whales voting WAAAY less. Just that alone doubled the curation rewards I was getting prior to that.

Some of it has to do with time frame. But it ends up being something that needs to be played with, especially while holding some SP. There are multiple factors right now that allow for better curation rewards compared to before like the fewer whale votes and the share price going WAAAY up. When steem was at 7 cents, there just weren't that many rewards to pay out.

Sorry I can't give specifics on this for you. The best I can offer is to try to build up your SP again and I can follow along this time to see what might be going on.

Right now the slider bar shows up once you have 482.426 or more SP.