Pay per packet is pretty interesting approach but I am not sure how really practical it is. Usually, billing happens for bandwidth, not by counting packets.
Discussion
I'm not hard-set on the per-packet concept. Bandwidth would be fine. Packet-level seemed more commensurate with payment channels so it came to mind first.
I might be wrong about that, though. Perhaps bandwidth is a more similar concept to payment channel capacity?
I think that "base fee" can be used for per-packet processing and "fee rate" for bandwidth.