11gR2 Trace file(s) not created for dbms_monitor.serv_mod_act_trace_enable call

This question relates to Oracle Enterprise Edition 11.2.0.4 on AIX.

I'm trying to help tune an application where we have application servers are firing queries and calls to PL/SQL package procedures and functions at the database.  We have most of their calls doing the latter, so I've edited the called packages to include a simple dbms_application_info setting line right at the top of each procedure function:

...

BEGIN

  dbms_application_info.set_module(module_name=>'$$PLSQL_UNIT',action_name=>'$$PLSQL_LINE');

...

In tests, I have used "dbms_monitor.serv_mod_act_stat_enable(service_name=>'SYS$USERS',module_name=>'MYPACK');"  and can see the resulting entries in the