Configuration of nagios plugin path

I tried to configure the location of nagios plugins like described in https://docs.observium.org/config_options/

so I set 

$config['nagios_plugins'] = "/usr/lib64/nagios/plugins";

because in centos8 it is located in /usr/lib64 as described but it didn't work. So I search through the source code but looks like this variable isn't used anywhere. But I found 

$config['nag_plugdir']

so I set this to the correct path but didn't help. 

At the and I made a symbolic link in /usr/lib to /usr/lib64/nagios and voila, all plugins are working. 

Can you correct the documentation please how to configure the plugin path the right way?