Desire to improve the printed page size of a booklet.

I use a Brother 8860DN printer to print booklets on 8.5 X 11 letter-size paper. Each 8.5 X 11 sheet of paper contains 4 LibreOffice Impress note pages – 2 printed pages on each side of a sheet of paper. Each printed page goes on a 8.5" high by 5.5" wide section of paper.

My problem is that the printed note pages are too short to cover the whole 8.5 inches vertical height of paper. A frame-line prints around each page with a 0.25 inches margin (correctly.) But the vertical distance between the Impress header and footer is only 6.25 inches as printed – leaving the printed page almost 2 inches too short compared to the paper it is printed on.

How can I lengthen the header-to-footer distance to make it fit the paper better?

Windows 10, LibreOffice Version: (x64)