Which wp-config.php? Root or subdomain?

I see the standard reference to the code to be added to wp-config.php but there are more than one wp-config.php file:

1. The wp-config.php file in the root directory.
2. The wp-config file in the subdomain directory.

Folder Structure

Public_html Root (primary WP installed here and active. Call it WPA and it is NOT a multi-site.)
Subdirectory – contains an add-on WP not at all related to WPA. Call this instance WPB – this is a domain based multi-site.

In this common scenario wp-config.php exists in both the Root and in the Subdirectory folders.

So. 2 wp-config.php files and 2 instances of WP.

Does the Root directory version of wp-config.php have any impact or is only the Subdirectory version of wp-config.php used in the multi-site situation?

Multi-site specific subset of code:

public_html config file:

/* Multisite */
define( ‘WP_ALLOW_MULTISITE’, true );

define(‘MULTISITE’, false);
define(‘SUBDOMAIN_INSTALL’, true);
define(‘DOMAIN_CURRENT_SITE’, ‘webdezein.com’);
define(‘PATH_CURRENT_SITE’, ‘/’);
define(‘SITE_ID_CURRENT_SITE’, 1);
define(‘BLOG_ID_CURRENT_SITE’, 1);

Subdirectory config file:

/* Multisite */
define( ‘WP_ALLOW_MULTISITE’, true );

define(‘MULTISITE’, true);
define(‘SUBDOMAIN_INSTALL’, true);
define(‘DOMAIN_CURRENT_SITE’, ‘webdezein.com’);
define(‘PATH_CURRENT_SITE’, ‘/’);
define(‘SITE_ID_CURRENT_SITE’, 1);
define(‘BLOG_ID_CURRENT_SITE’, 1);

Thanks,

Jerry