Change size or image for mobile phones

Been struggling with this a bit.

I have a background image I use for Parallax, it works well (graphically) on landscape devices, but on phones, they are too small.

I have tried a few different options. But if I make it larger (using css
.nk-awb-wrap
transform: scale(1.5);
), but that breaks the parallax completely.

I have been thinking I could use an alternative picture, but can’t figure out a way of telling AWB to use a different image when on the mobile, the only option I can find that is responsive is turning Parallax on and off on mobile devices.

The page I need help with: [log in to see the link]