This hasn't been a problem yet, but I fear it might become one with the increasing number of players. All I want to do is suggest an addition to the current rules regarding champ spawn etiquette. If one player or a group of players is attempting to complete a champ spawn, while another player shows up to to try the champ, the player that just came to the champ sould leave as soon as he notices that other players are already there without trying to join them. If the players noticed that someone else has shown up and left, then they could of course ask him to come back if they need the help.
If there is already a large group of players at a champ, the last thing they would want to do is split the loot with an extra person who wasn't there from the beginning. However, they wouldn't want to be mean asking the other player to leave. This rule would prevent that from ever happing. Hope you consider it.

If this doesn't make sense then let me know what part you don't get and I will try to clarify.