I don't like that cache system they have. It basically forces everyone to receive from the aggregation cache, and write to the user's defined servers. You're not the only one I've heard complaining about that cache. And there's nothing you can do to disable it, and just receive from your relays. That's why using different relays makes no difference because your read requests are automatically being handled by the cache server. Your relays don't even come into play unless it's a write request.