Hi Andy
The image is designed to be used with a background image and not a text/logo image as the image width/height ratio will appear to change to fill into the screen area of different devices and browser windows. This means that depending on the visitors screen size some parts of the background image will be cut off at the top/bottom or at the sides.
There is a different setting for the site logo which can be found in ‘Appearance’ > ‘Customize’ > ‘Site Identity’