The center is best but being on the map is fine. Just think about what part of your driving you are doing at the edge. For example, if you are running a sort of large turbo that is starting out at the edge but then getting into the sweet part of the map, that is fine. But if all you ever hit is the edge, you may want a different unit.
97 Laser Red GT-248A Wingless model, Built Lincoln Mark VIII motor-Procharger D1SC, 3 core IC
2012 Black GT-Saddle, 3.73s, Brembos, Shaker1000