iOS Safari address bar behavior

I'm noticing inconsistent behavior of the address bar on my iPhone's Safari app. After loading the page on some sites the address bar will stay for 2 second and then rolls up to give more space to the page. On other sites, the address bar stays until you scroll up. For example, Google annoyingly does the roll up behavior so I end up finger tapping the wrong result. The Verge, on the other had, doesn't do that and I can click a link without fear of the page jumping up a centimeter. Is this a website specified behavior or is my Safari just acting weird?