I have several instances of the same service running on one server, differing only by TCP port number (think: several Apache/FTP/SSH instances, one instance listens on port X and second on port Y).
I have created "parent" template with items/triggers/graphs to monitor one instance on port {$MY_PORT}.
Then I create "child" template that links to "parent" template and sets macro {$MY_PORT} to a specific value.

My idea is to have one place to add new items/triggers/graphs ("parent" template).
For every instance I create "child" template and just set macro {$MY_PORT} to actual port value.

Problem:
when I try to link two "child" templates (which differ only by macro) to a host I get an error:
Template "Perforce Replica 1110" with item key "p4.replica.files[{$MY_PORT}]" already linked to host.

"Perforce Replica 1110" is one of child templates with macro set to port 1110

What is the right way to monitor several instances of a service that differ only by port number?