I've read some literature on mixing in systems like TOR and also in Bitcoin. In Bitcoin and Cryptocurrency Technologies, the authors explain that uniform transactions are highly important in order to prevent correlation attacks by matching inputs and outputs:
Uniform transactions. If mix transactions by different users had different quantities of bitcoins, then mixing wouldn’t be very effective. Since the value going into the mix and coming out of a mix would have to be preserved, it will enable linking a user’s coins as they flow through the mix, or at least greatly diminish the size of the anonymity set. Instead, we want mix transactions to be uniform in value so that linkability is minimized. All mixes should agree on a standard chunk size...
However, I'm unable to find examples where this is visible in the blockchain.
I've also seen mixing in Bitcoin described differently, for example in the Bitcoin and Beyond paper:
The mixing service aggregates bitcoins received from all its users to re-distribute them again. Some services use randomness, i. e., they split the amount into smaller random chunks and transfer them after random intervals. The user can schedule the transactions and provide time constraints.
Now I'm looking for examples of these types of mixing transactions in the blockchain, especially one where I can see a fixed chunk size being used. Is one of these schemes used more frequently nowadays?
Is the second scheme really secure? If THIS is actually mixing like I assume, then isn't it possible to match sets of inputs to sets of outputs that have the amount (or slightly less) BTC value and therefore have to be connected? I can imagine that this does also work over the course of multiple transaction in case the payout of a mixer is split into intervals.