Electromagnetic interference is identified when visible grey dots are seen along the Touch Sensor borders or spread over the Touch Sensor active area.
As you increase the Shielding level, you are reducing the electromagnetic interferences. The grey dots tend to disappear as the shielding level is increased. As a consequence, the touch recognition may be less sensitive. However, increasing the Shielding level may be required to avoid false touches. The shielding level should be maintained as low as possible.