most clients are pretty random... some probably feed off relay data spidering services even... with how they select your relays
the client-focused solution is contained in NIP-65 and requires NIP-42 to gate access on read and write side for various reasons i'm sure you are aware of
i keep hammering at NIP-42 because i see it as the biggest blocker for progress right now, and until every client supports it i am not gonna stop screeching at the client devs, i have even been blocked by one or two so i'm not unaware of how repetitive i'm getting