Call for Contributor & Donor Input RE: Cashflow treatment decision

Cashflow from the "50% of 10%" of post-revenue, that is income ex-posting costs, is normally small and volatile. IMHO, it's so trivial, it's noise and barely worth this thread. Last month, we had a record setting post, (thanks to) 619793 @Undisciplined. We don't get an isolated number for these posts, but the territory likely earned ~5K from that post.

I want to capture this inflow for the montly fee-post-cost-adjustment, in a way that doesn't increase volatility in posting costs.

Any ideas?

The one option I can think of, would be to declare a trailing moving average of ex-post-cost-income. Include the term in the post-calc-change logic each month, assuming the MoM growth = 0 %.

Also, bonus points for ideas that are simple to track or screw up.