Normally when you pluck the string near the bridge you get more treble and a thinner sound. When you pick towards the neck the sound becomes fatter with increased output. There is less string vibration closer to the bridge as compared to increased string vibration towards the neck position. With increased string vibration, the string moves more magnetic field back and forth within the pickup and you have increased output from that position. The harder you pluck the string increases the output and attack. If the pickup is quite close to the strings the harder you pluck the string can cause distortion in the pickup. If the pickup is lowered, you will notice a smoother sound but with less output.