There is a tendency, particularly among controllers who are used to having the best transmitters and receivers, to believe that if party A can hear party B's transmissions, and party A can hear party C's transmissions, then party B can hear party C's transmissions. Radio, I'm afraid, doesn't work like that all the time.
I've certainly come across situations in which the plate tells me to "Contact X on passing xxxx ft", but it's extremely unlikely that I'll be able to hear X's transmissions until I'm thousands of feet higher. Hence the only thing I'm likely to do is step on one of X's transmissions.