Your license sets the absolute number of concurrent users. The required -gm switch limits the number of concurrent user connections on a particular server.
The -gn switch sets the number of execution threads that are used for the catalog store and connectivity while running with multiple users. It applies to all operating systems and servers.
On Windows, start_iq calculates the value of this parameter and sets it using this formula:
gn_value >= gm_value * 1.5
Set the -gn value to at least 1.5 times the value of -gm. Specify a minimum of 25. The total number of threads cannot exceed a platform-specific maximum; see -iqmt num for details.