> We used the “percentage-rejected” metric minus the false negatives to ballpark the $1.7 million total annual savings.

I think this may too sanguine for the false negatives in that it ignore latency sensitivity. Generally, batch processing (like preview generation during pre-warming) is cheaper than latency sensitive processing (like preview generation when the user is waiting for it). If you don’t take that into account, you can be misled by your cost metrics.