Narrative
The per-stream rate clients quote you doesn't exist.
Clients will often arrive with a per-stream rate they found online and a simple sum: × rate. When the statement doesn't match (and it never quite does, even when the stream count holds steady month to month) they want to know why.
The figure they found is usually around £0.003. Multiply it by the streams, compare to the statement, and the numbers diverge. Not by a little.
Here is what to tell them: that rate doesn't exist. Not as a price, anyway.