PHP and CGI have the same base path: /home.
To make sure you stay pointed at the right location, use the PHP-standard $_SERVER['DOCUMENT_ROOT'] value to refer to your site's public directory.
We also provide the $_SERVER['NFSN_SITE_ROOT'] variable for this purpose, in addition to DOCUMENT_ROOT. NFSN_SITE_ROOT points to your site's root directory, the parent of public and protected, making it the best choice for safely referring to the protected directory from PHP.
We strongly recommend that you use $_SERVER['DOCUMENT_ROOT'] or $_SERVER['NFSN_SITE_ROOT'] whenever possible and avoid hardcoding paths in order to avoid problems in the event of a change.