Redirect to users blog but already subscribed


I saw a previous post with the redirect to the users blog. My only problem is when a user signs up, they are automatically a subscriber to the main blog and to support sites that I created.

When I use the redirect code, it things that my main site is the users primary blog.

How do I get them to login and actually redirect to the blog that they created rather then the blogs that they are subscribed too?

Here's the previous post I was referring too: