I would guess "SRTP" is just the shorthand for something that's less simple than that sounds. It likely has some "starvation protection" in the same way that a typical priority queue does. Like having in-queue age time bump up the priority.

From my understanding, this is total message size, but packet. If a receiver has two incoming messages, a batch upload and a query for a list, the batch upload may have 10MiB to transmit while the other message may only have 1KiB. This, to improve latency, the smaller message should be prioritized.

You can avoid starvation by increasing the priority of a job (an RPC in this case) when it hasn't made progress for a while. Or you can do weighted scheduling where the shortest job has a higher probability of being scheduled (e.g. WDRR) instead of absolute priority.