With a List View instead of a Form View, a report layout based on your Tbl_items table should do what you want here. You should be able to resize the body to be just a narrow row for your Items fields and the related fields from the other two tables can be placed in other layout parts such as headers, sub summary parts, etc. Also make sure you haven't set the body part to have a page break before every occurrence or a page break after every 1 occurrence.
PS. Portals do slide, but they have limitations. You can set a portal to slide up to remove space for unused rows in a portal, but you can't Slide individual fields within the portal. Also, if you get so many items that your portal can't show them all at the same time, they'll be invisible when you print the layout--all issues avoided with a list view layout based on your items table.