Even though the relays are reliability-wise identical, their position within the diagram matters. This is best illustrated using the following reliability importance plot. It can be seen that even though all relays are identical, a specific relay failure affects the system differently due to its position within the system.

 

Specifically and in order of importance, the greatest impact is if 2 or 5 fails followed by 4 or 3 and then by 1 or 6.