Converstion tracking question

I'm setting up a goal in GA for ProSites and Iin the past I've used the IPN link as my conversion link for completed payments. In ProSites the IPN link is to the admin-ajax.php page on the back-end. I'm wondering if I use that address will that be the proper thing. I want this conversion to track the completed purchase not the checkout page.

What do you guys think?

Thanks