Page header, responsiveness

Hi,

I am trying to have a different image (in full screen) in the header of the pages, with no text - just an image.
I am using add-on page header (or also tried to add the image using GP-Hooks).

The issue is that it is not responsive. Image does not resize but is cropped for smaller screen sizes.

Why is it this way? Is it because it is a background image? And if so why does it have to be a background iamge and not just an image? Sorry about my ignorance but I am puzzled as to why it does not work.

Note: I have tried as a workaround to use sections with an image in full screen and that works fine and resizes too. But then I find many other restrictions like not being able to add sidebars to my pages or the image not showing on protected pages unless the member is logged in. Not ideal.

I am open to suggestions as to how to achieve this please. Keeping in mind I need sidebars and password protected pages...

Using GP Premium 1.2.92 and wordpress 4.7.1.

Thank you