Can not understand. Is that just a scheme and server is capable of mixing coins from any numbers of parties or it actually mixes UTXOs belonging exclusively to two parties? To test, can I mix the coins from my own but three different wallets?
Terminology is a mutex in the lexicography of Bitcoin where we equate many views of the same operations with only one truth rather than an expanding model including differential references. UTXO's, true but in the mind of the user that is a wallet address, in many cases several UTXO's a set of even if some are reused.
Let m e establish a testing protocol if you have some Bitcoin to mix anyway and choose to participate. This is suggested because I do not have the answer, there are two intermediate buckets in the diagram, however, an undefined limit of input sources to those buckets, even where the relationship to the bucket is undetectable we suppose, and that the return from a mixing deposit transaction is not immediate but with some delay, so to establish a mixing session and then make multiple deposits immediately subsequent to each other and all greater than 0.005 BTC in value, then to observe or better to analyse the resultant returns. Often, I am mixing en-route concisely with the making of a payment in which case my wallet is certainly disconnected, but, I am still able to monitor the receiving address(es). If you consider?