HP L 5 manual How the Printer Tiles a Pattern

Note	For efficient memory usage and improved performance, it is strongly
	recommended that user-defined patterns should be 8x8, 16x16, or
	32x32 in size. Specification of patterns that are either 1 pixel in height
	or width is strongly discouraged.
	If user-defined halftones are also used, they need to be either the
	same size or multiples of each other to avoid render anomalies due to
	each pattern being rendered differently across the page (if tiled), or
	due to variations
	in xy position.

How the Printer Tiles a Pattern

A user-defined base pattern is a rectangular binary pattern stored in the printer. To apply the pattern to an image area on the page, the printer duplicates the base pattern across and down the page. This process is referred to as tiling. (The pattern is only applied to those areas on the page for which the pattern is required.)

5-34 The PCL Print Model EN