A visitor should be able to move from a project to an article without searching again for the way around. The header is a landmark: its position, scale, and behavior tell people which parts of the experience remain familiar. The content below can then vary while visitors still know where to find the menu.
Keep your bearings.
When a reader moves from a project to an article, a stable header tells them they are still in the same place. They can look in the same position for the menu rather than relearning the page. They can give more attention to the new content because they already know how to navigate. The illustration holds the header in place while replacing an image-led project with a text-led article. The reader can recognize a new kind of content without interpreting it as a different site. Keeping navigation familiar lets the work vary without making the site harder to use.
Put it into practice.
Compare a project, an article, and a form at the same screen width. Keep the navigation in the same place with the same behavior. Let the main content establish its own hierarchy, and check that the shared header neither competes with it nor hides it.
Which parts should remain familiar as the content changes?