All right, so what the
Sparrow's Premix Fee Rate do is to set 2 things. First, to set the Tx0 miner fee, and second, for the miner fee contribution (
premixer, the one who pays the fee of the coinjoin tx).
Correct. Although note there are not two separate sliders as the GitHub post you linked. Rather, there is one slider, which affects both Tx0 and the premix UTXOs:
https://github.com/sparrowwallet/sparrow/issues/895#issuecomment-1477389172So in the event that the on-chain fees dropped while the user had broadcasted/initiated the transaction with some set of
Cycle Priority(miner fee contribution). Whirlpool coordinator adjusts/make-use-of the, if there are any, excess transaction fees by adding up more input/output. With a minimum of 5-inputs/5-outputs and a maximum of 8-inputs/8-outputs.
Also correct.
Yes. There are three fees you need to consider altogether. The first is the fee to Whirlpool itself, which is a flat fee depending on the pool you are joining. This fee is dependent only on the pool you join and does not change with the amount you are coinjoining, so becomes cheaper overall if you coinjoin more in one go. The second fee is the network fee for Tx0, which splits your initial input(s) in to the necessary size to join the pool in question. The more premix inputs you create the larger and more expensive Tx0 will be, but it will still be much cheaper to create one Tx0 creating 20 premix inputs than it would be to create four Tx0s creating 5 premix inputs each. And then the last fee is the additional amount attached to each premix input to pay for its first mix. This is the only one that doesn't get cheaper the more you coinjoin, and will scale linearly with the number of premix inputs you create, as each one needs to pay for its first coinjoin.
But then of course once you've done all that, you get unlimited free remixes.