+LCD Calibration Settings in ColorMunki software
LCD displays only provide control over brightness. There is no bias or gain or contrast adjustment. The only variation is the intensity of the backlight.
If you are having difficutly with the contrast adjustment in the ColorMunki software, try resetting your monitor to factory defaults. Skip the contrast step, even if your monitor has that control. Then, adjust your brightness to reach your target. If you find that you cannot reach the target using your monitor's brightness control alone, raise or lower the contrast control as needed to help fine-tune your luminance range. After you reach the brightness target, proceed with creating your ICC profile.