Changing config file path in Codeigniter

My folder is structured like this:

- root folder
    - config
      
      config.php
    - MySite
      - system
          - application
             - config
                 config.php

Within application folder is the config.php file, I have modified it so that it loads the config file from config -> Config like this from the root directory:

<?php 
require_once('config/config.php');

The config file works fine if I leave the config file in its native directory application -> config -> config.php but as soon as I try to lead it from root folder -> config -> config.php, it throws up the following error:

> An Error Was Encountered >
> Your mysite/system/application/config/config.php file does not appear to contain a valid configuration array.

Any idea why this is happening, and how I can resolve this?

Thanks