Could it be there is a mistake in your pricing example:

    (e.g. 24 t-shirts with 1 color front & back print is $8.66 + $0.25 = $8.91/ea)

The table says 24 shirts, 1 color is $7.28. 2 colors is $8.66. Should it be 2 colors? Or does one color count for two when used front and back?