Is it the first miner to send the file or to complete the file send who gets paid?
Do you mean for retrieval mining? If so the idea has been to use payment channels where the client sends incremental payments as the retrieval miner sends incremental parts of the piece requested. So if a client opened up multiple retrieval requests they would pay miners in parallel for them to the extent that the miners returned data. This is, however, not finalized. Presently the way the code works retrieval is free.