BTC (AUTO) works by mining X11 coins and then they are traded and to BTC. If those X11 coins are not doing so well against BTC  in regards to their value, then price falls.

If you look in the last week for example, Dash coin prices were in a pump so you got more BTC for your coins and now Dash has fallen again so that is why payouts go down.

Perhaps sometimes it might be better to mine Dash or Start coin on their own and hold them and then wait for their values to go up and then sell...

That choice is upto you though.