Tooltips contain only name of item and preview
Same as for informational panel: preview of files depends on amount of screen size is used to display file size. It depends on file icon size. At least with my settings preview on tooltip (and on information panel) is bigger than preview in the central area.
Of course, there's not much point to use preview on informational panel, tooltip and big file icons with previews enabled at same time. But user can choose between these options those that are more convenient for specific user.