Combine last on top and first on top to force fixed elements to be in front


When I assign bring to front to an element, I expect it to be in front.
But as I’m using auto-layout, with fixed position elements, everything depends on the first on top/last on top option. As I’m having top elements casting shadows to elements below (I think it’s very common pattern), I can’t have at the same time fixed element in my page.

Anyone has a tip to deal with that without destroying all the auto-layout structure of my page that is so useful ?