How to protect the blog page with Membership?

Hi,
I'm using Membership in a website with 4 different access levels and my blogpage is not working as I would like.
I have created 4 post categories and have assigned each category to an access levels through Negative Rules; that protects my categories archive and my posts but not the blogpage, where all users can see all the blogpost titles & excerpts (including those assigned to other categories/access levels).
Am I missing something in the Membership settings?
Thanks in advance,
Xènia