As more relays pop up that are aggregating/broadcasting to and from other relays, the list of relays that a user is directly connected to in their client will become less and less useful for determining how to get good coverage of that users posts.
The list of relays that my profile shows i’m connected to is only part of the picture, since several of the ones i’m connected to are broadcasting to others.
Instead, the way to determine that will probably be by using “indexer relays” like nostr.band that scour all the relays to find which ones a user’s posts have been seen on.