Even without that feeling, sticky headers kill the feeling that I'm moving through a viewport of a webpage. It makes your website look like it's not of the "webpage" medium that I've been familiar with for 20 years. Humans have a very good eye for relative movement. The visual processing part of your brain considers movement much more contrasting than color. So a fixed header when you're scrolling at 1cm/second is visually equivalent to a big bar moving upward at 1cm/second while you're trying to read an article. It's hard not to pay attention to it. But navbars don't contain content, so they shouldn't steal attention from the page content.