PHP settings can be different for sites (for different users).
Since, for example, when using PHP mode as CGI, user have own php.ini and can change some settings or manage PHP extensions through ISPmanager.
You can create phpinfo script in the www site directory (file.php)
PHP Code:
<?
phpinfo();
?>
and see all data including the paths to files and directories, and other parameters by opening this in the web-browes.