Rather than asking it to be scaled in the printing process, I'd recommend creating two different files to a specific size. Although the paper sizes are the same, unless the margins differ, the aspect ratios of the two image areas will be different. That is because you are subtracting fixed dimensions from variable dimensions of a rectangle. I always create the proper size file and have "Scale to fit media" turned off. That way no additional interpolation is needed when it is ripped. The difference in aspect ratios and/or your margins in page setup are the likely culprits.