The “hero” image is the featured image at the top of your instance homepage. It should be a minimum of 1200px by 600px
The aspect ratio shifts from 2:1 on mobile to 3:1 to make use of wider screens. So if you have content you don’t want cropping out (like a logo) you will need to make sure it falls in the vertical center. See diagram below, red areas are only visible on mobile, blue is visible across all screen sizes.
Here is an example in situ, note a small overlap with the text box below of about 20px
