Html post form action does not specifically specify php file?

I have a post html form and action is index.php which is the main page of websites. I never had index.php in the address bar since the "/" links go to it, and even if I did, it would be site.com/home(/) since I'm using the rewrite rules. This way, the user should never see index.php. However, the form submission does not work unless the action has a specific index.php, "/" does not work although index.php allows it. Any ideas on how to get around this?