breakpoint change on different resolutions

[Fabbryzz]

Hi, I tried to implement this plugin in a project where I make a map in full width and content scroll behind it.
I have encountered an issue on different resolution, the breakpoint isn't the same on resize of window or on mobile resolutions.
Look at my test page: http://fabbryzz.it/test/storymap.js/
Can you help me to resolve this? Thanks a lot!