adjusting audio levels in iMovie 10.0.7

Trying to moderate the clipping in one of my videos. Choosing "loudness" moderates the volume level but does not entirely remove the clipping. In older versions of iMovie, one could grab the blue line and adjust it in 1 or 2% increments. In my version it's 25 or 34 or 40 or 85 or 100 or 112 and nothing else. Am I just seeing Apple glitch or am I doing something wrong?

In the same vein how do I get to a prevision trimmed for audio?