The easiest way to adjust the length of the audio fade without monkeying up it's level setting is to select the clip on your timeline and then click Adjust to open the Adjustment panel.
In the clip's Adjustment panel, open the Volume listing, click the Show Keyframes stopwatch to open the keyframe timeline and then just drag the position of the diamond-shaped keyframe further from the end of the clip.
Thanks! Also, you know what I just found..? Check out the tooltip in the very bottom left corner of my screenshot; right above my start bar.
Great tip, clanderson!