I think there must be a "check six etiquette"
I mean, no doubt that if I gave a check 6 is my intention to help a mate, but throwing check six, as soon as I see an enemy plane in range is worse than not givin it , maybe.
In furball situation is very hard give correct C6 , and who receives it may loose precious time, if they are not correctly related to his situation.
Maybe the use of AH voice can help to be more precise?