In most cases, Divi layouts are created using the default Desktop mode:
This means the layouts are perfectly optimized for Desktop devices however on smaller screens they might look slightly different.
The main reason is that by default all the responsive options inherit their values from the desktop view.
To understand if a particular option can be optimized for small screens look for the cell phone icon next to the available options:
Once you click the mobile icon you will see three tabs where you can define different values for Desktop / Tablet / Mobile devices.
Keep in mind that if you don't define a specific value for responsive options, then by default they will inherit the values from the Desktop view.
If you want to optimize some general settings site-wide then you should go to the WordPress Dashboard > Divi > Theme Customizer > Mobile Styles options: