To add a fade in or fade out to a video clip, right-click on the clip on your timeline and select the appropriate Fade option.
What computer operating system for your Premiere Elements 13/13.1?
Since you are asking about "enhancement of fades" and not how to add fades, I offer the following.
When you apply the audio Fade In, two Volume keyframes are automatically placed, one at the beginning of the clip and the other 1 second from the beginning. If the clip is using the default Volume in its Timeline audio clip title bar, you should see those two keyframes represented as white dots on the Timeline audio clip's rubberband (orange line that runs horizontally across the clip). Please refer to screenshot. If you right click the Volume keyframe (white dot) at 1 sec in the audio file, you will get the choices that I believe you seek.