If you are finding that your images are not cooperating for you within Sonata, checking out this doc might be a good idea.
Images must have a width of 600px to work properly - no more, no less. Any images with a height greater than 350px will be squished. The sample images are 600x200px, so we highly recommend sticking with those dimensions.
The 'break' between articles and the next image is created by a combination of "background color" and "top padding". This can be edited by viewing the 'source code' inside of the 'Email Main Body' module.
If your image is not 600px wide and does not reach the edge of the document, the desired outcome will not be reached.