Gable end: they’ll see it more miles, but from only one direction.
Front of barn: they’ll see if driving past from either direction but the view will be briefer.
Lower wall: cheaper and safer to install but the setting may be compromised when the corn is 8 feet tall.
North facings: are protected from the fading rays of the sun, but are in shadow during the cold months.
South facings: are lit brightly all year, but will fade more quickly.
Distance from road: an unobstructed brightly painted 8 foot square barn quilt will show up at a long distance but there are limits.