Thanks so much @russian-dima . Yes works pretty well on your demo site.
In the header, I did have a hidden text element. After removing it the header has now collapsed a tiny bit more. I now just have a logo image, horizontal menu and login bar. I have tried removing absolutely everything but the strip still remains.
Interestingly, I have played around with reducing the height of my header.
As soon as I make it below 70 px, the header strip collapses significantly more.
Btw I don’t take credit for this code. I got it off from another post.