additional directives for php.ini of subdomain are not being picked

[javismiles]

my subdomain has a php.ini in
/var/www/vhosts/system/domain.com/etc/php.ini

which says DO NOT WRITE because will get overwritten etc

ok great
then i go to plesk panel and i go to PHP settings and i go to extra php settings, additional directives
and i add there
session.cookie_domain=.domain.com

and i restart apache
and i go look in php info
and of course it is NOT there

so why is not there?
so what is the point of the extra directives?

this is for a subdomain of a domain

 

[DRY411S]

When you go look in php info is it including your /var/www/vhosts/system/domain.com/etc/php.ini file ?