Oh, that is pretty easy to tackle. My guess is that you are using the Gallery post format. If so, Suffusion is set up by default to tackle the Gallery post format differently. It shows one large image and a handful of thumbnails on an archive page (i.e. the front page or a category page), then upon viewing the full post you see all the images.
You can turn this behaviour off: Appearance → Suffusion Options → Other Graphiical Elements → Post Formats → Posts ('Gallery' post format) → Disable Gallery Post Format in archives. If you wish to keep this behaviour you have options to customize it in the same section.