PHP 7 as PHP-FPM application, user and groups are www-data

I would like to switch from FastCGI application to PHP-FPM, but if I do so from the PHP settings of a domain that I manage under Plesk 12.5, the user that is executing the application is www-data, this causes problems of permissions with the FTP user files, which is the user that the FastCGI setting makes PHP run from.

I can verify this in my PrestaShop application, since the .htaccess file cannot be overwritten by PHP running PHP-FPM, if I manually delete it, I can see that it is generated...

PHP 7 as PHP-FPM application, user and groups are www-data