You might need to use a wider layout size. It’s the same sort of idea when laying out pattern pieces to cut… generally the wider the fabric, the less fabric it takes overall. If you select a layout size that’s too narrow, you may only get 1 pattern pieces to fit across the width, so the program places pieces on another layout sheet - thus wasting space.Maybe play around with not allowing certain (larger?) pieces to rotate may help to save space.
If you’re printing a tiled PDF you have to think in terms of multiple sizes of the printer paper… like if using 8.5"x11" you might use a layout size of 34"x44" (minus the margin overlap - could be like 33.25 x 43.25 depending on printer margin size)… a 4x4 matrix/16 sheets of 8.5x11.