On Merlin Chain, accounts follow the EVM model, so fan-in and fan-out show up as many addresses paying one account or one account paying many. The address format says nothing about intent.
Counting senders and receivers
Count the distinct addresses that feed a single account, then count those it pays onward. Short gaps between inbound and outbound transfers matter most. Merlin Chain also sits on a ZK-Rollup, so read the order of events from the public explorer and not from your own assumptions.
Phrasing the pattern
Describe pooling followed by redistribution and attach the hops you resolved. Leave out the word mixer unless your evidence names a service.