two schools of thought really.
A thinner one with a large surface area will be more effective than a smaller, thicker one, even if both have the same tube surface area. Because like that book says, the air heats up as it passes through the core so has less cooling effect towards to back of the core.
However, a big thin one which is mostly obscured behind the grill, bumper etc... will be less effective than a smaller, thicker one which is fully in the cold air flow.
so it's swings and roundabouts really and depends what you can fit on your car. If fact the radiator being right behind it will further restrict airflow too as if the warmer air can't get out of the back of the core quick enough, fresh air can't get in at the front.