FFP's anual salary expenditure

Hello everyone!

I am managing Chelsea and I have noticed in the FFP tab that the Allowed Yearly Player Wage Expenditure is fluctuating every year. The 2015-16 season I had €275M per annum as maximum allowed, and in 2016-17 I am having €240M. My current spendings are still bellow that, but I don't know if this will still be the case if there is another decrease next year.

So my question is, is there a reason behind this decrease? Is that amount somehow dependent on my team's financial status? Is there a way to make sure that I can keep this number from further decreasing?
I would like to get a better understanding of this.

Thanks in advance!