Hi,
The value of the z-index of that box is based on mostly customer feedback. In most cases this value works the best. Lower values caused the box floating below certain page elements for users that use page builders with interactive elements. Unfortunately there is no good value to use, this is the least problematic in most cases.
You can change the z-index of the results box under the Theme Options -> Custom CSS panel: https://i.imgur.com/kcj77MJ.png
