I don't recognize what you mean by "clicking the slider". Are you selecting an option in the position section of the inspector labled "Slide objects up based on"? Setting the portal to slide up with the "also resize enclosing part" option selected. Should produce the result you want when Previewing, printing or saving as PDF.
Sliding portals have limitations. An alternative approach that can be more flexible, is to create a summary report based on the portal's table with fields from the parent record placed in a sub summary part.