I see lot of websites that has design responsive for all devices, with css styling that as a user [, designer, and developer] can say that put effort upon. They use a banner/header/menubar on the topmost part of the site. There are with 35px or less thickness, other with 50 or more. Some has search fields on it, while other don't. Some has menu items, others have logo.
Im not asking when to use a stick top bar and when should not. I'm asking on what should be the criteria of a top bar for it sticky-"certified". They say that any top bar that is not for mobile devices are qualified, but I have seen good mobile designs using stick top bar. Some says make it first thin before gluing, but some thick banners are sometimes glued.
Sometimes there are thick banners but when you scroll down, it glues at the top edge and becomes thin. Yet there are some thick banner that when you scroll, are glued but are not shrink-ed. Yet there are some thick banners that are not glued at all... What's with the first two banner that is not found on the third banner for the developer of the third banner not to make it sticky?
I believe that even if all reasons are there for a designer to make a top bar sticky (e.g., it contains vital navigation links, etc.), the designers still leave it as is because of "these certain criteria".