Applied Pi calculus: Evaluation context that distinguishes replication with different restrictions

For an exercise, I need to find an evaluation context $ C[\_]$ s.t. the transition systems of $ C[X]$ and $ C[Y]$ are different (=they are not bisimulation equivalent), where $ X$ and $ Y$ are the following processes:

$ $ X = ( \nu z) (!\overline{c}\langle z \rangle.0)$ $ and $ $ Y= !((\nu z) \overline{c}\langle z \rangle.0)$ $

Intuitively, the difference seems to be that in process $ X$ , all replications of the process output the same $ z$ on channel $ c$ , while in process $ Y$ , all processes output a different $ z$ . Is this correct? And how could this be used to construct an evaluation context such that $ C[X] \neq C[Y]$ ?