Recreating Revenue Sum Formula

I had an original requirement that was to gather the sum of the last 3 months of revenue and multiply by 4 to return a value. I have perfectly working solution that is this:

However there has been a recent change in requirements. End users now want to implement using date slicers, so they can see the revenue at any point in time. So in my date table, I have Month and year slicers:

So now my issue is, if I select months 4, 5 or 6, my above formula will return the sum for the particular month selected since those months are the last 3 completed months, but if I select month 2 and beyond it will return blank which is expected.

How can I restructure my formula so by default it will return the last complete 3 months of revenue, but if for instance I select just a single month from the date slicer, it will give me the last 3 months of revenue from there?

So if I select month 3, it would give me the sum of months 1-3. If I select month 5, it would give me the sum of months 3-5, etc. etc.