Hello Dan,
It will not be possible to see the whole image on mobile depending on how much content you have in your Welcome section.
The image will adjust to be 100% of the height of the Welcome section which means if it is wide some parts will be cut off, otherwise the image would be distorted.
You can always add custom CSS code to reduce the font-size of the text on mobile so the Welcome section is smaller, which will mean more of the image will appear.
Can you provide me with a link to your site?