custom url – permalinks

Hello,

I developed a new web site, all seems to work perfect but I would like to improve something:

I created a custom post type called portfolio. Then I created two custom taxonomies called directors and represented, and the urls look like this:

http://www.mydomain.com/directors/director

but when I try to reach a post for a director like this http://www.mydomain.com/directors/director/project, wp change the url to http://www.mydomain.com/portfolio/project.

How could I change it?????

Many Thanks!