CUPS won't offset pages by 1 inch to the left

[jo]

I'm trying to offset my pages by one inch to the left (for book printing), the following command was issued in gentoo linux with cups 1.3.11r2:

lp -d pdf -o page-left=72 -o number-up=1 ~/principia.pdf                       [principia.pdf is my file]

My printer is a Brother HL-5250dn running the latest brother ppd file (installed via web interface). The following print command works in cups, so I know that the ppd isn't the problem:

lp -d pdf -o fitplot -o number-up-layout=lrbt -o DuplexNoTumble -o number-up=1 -o media=letter "$@"

An offsetting effect is observed when I do number-up=2. What am I doing wrong?