Custom Header non-responsive when shrinking in Desktopview

Hi,
I set up a custom global header for my site (not live yet).
The structure is an Image (my logo) and a menu.
I managed to create different view fitted to desktop, tablet and iphone within the module and row settings.
Now my problem:
When viewing the site on the desktop and narrowing the browser window in width to for example view two browser windows side by side, the image first starts to shrink as it is supposed to when scrolling.
But once I surpass a certain width, the image suddenly jumps to a larger size overlaying the content below. Also it will then be greater in height than the white background making it look really ugly.

When trying to adjust this in the theme builder, it will always switch into a custom view, which is no help to me either.

Can somebody tell me how to get this responsive to work when adjusting the size of the browser window on a desktop?

Thanks,
Cody