FYI Today NPR explained more about how it came up with the 15% drop in station fees. They voluntarily cut those fees:
NPR will shift station dues from a revenue-based model to one based on broadcast reach and households served, according to a report.
thedesk.net
Stations can opt into tiers that provide discounts for working with NPR on donor communication, among other activities.
current.org
As I've often said, NPR is overseen by its member stations. Not the other way around. The stations control the board of directors. So if the board wants to cut NPR revenues, they can do it, and NPR has to adjust its budgets. That seems to be what happened.
The previous system was based on CPB rules and guidelines. Now that CPB is gone, NPR can change its model as it sees fit.