greater lateral extent than either of the upper or lower regions 240 or 242 this allows each turn of the charging coil 208 to encompass a larger area which increases the gain of the coil 208 which in turn improves efficiency of energy transfer between the external charger 12 and the ipg 190 in other words and in comparison to the prior art illustration of fig2 b the loss of lateral distance within the ipg case 200 al is reduced or eliminated from a charging perspective the increased size of the charging coil 208 compensates for the increased distance between it and the top surface 224 of the case 200 third and perhaps most significantly when the charging coil 208 is mounted at the center region 244 of the case 200 the efficient of energy transfer from the external charger 12 to the coil 208 is made essentially independent of the orientation of the ipg 190 when implanted in a patient in other words it is basically irrelevant at least from a charging standpoint whether the ipg 190 is oriented within the patient with its top surface 224 toward the external charger 12 or with its bottom surface 226 toward the charger because the coil 208 is located substantially equidistantly within the case 200 the charger to ipg distance d see fig2 a is the same meaning that the amount of charging energy received is substantially.