Well, amxx.cfg is executed in plugin_init() from admin.sma ; and plugin_cfg() is sent at the time as plugin_init(), just right after (from same metamod forward) ; so considering it doesn't use server_exec() in admin.sma, it's possible config file to not be executed right away. Adding server_exec() in admin.sma or adding a small delay in your plugin, both should lead to same wanted result.