The front page 1 background image size is set in the atmosphere-pro > js > front-page.js file using
Atmosphere Pro Tutorials
The tutorials in this archive relate to the modification of default functionality and features included in the Atmosphere Pro child theme by StudioPress. The tutorials also enable you to add custom functionality and styling to this theme. The code is guaranteed to work as shown in the demo images and videos. Installation of all code as well as support for PHP code is provided for members.
This tutorial provides the code which enables you to add a unique image after the header on all page
This tutorial provides the code you can use to add a slider to the front page of the Atmosphere Pro