In TON's actor model, one wallet contract sends messages to many others, and many wallets message one. That is the shape of fan-in and fan-out here. The address format says nothing about it.
Counting senders and receivers
Count the distinct addresses that feed a single account, then count those it pays onward. Short gaps between the inbound and outbound messages matter most. Account IDs matter for sharding, since they route messages between shards, so read the order of events from the public record.
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.