How can i let a blob shadow (projection) fade out

I'm using a blob shadow projector in my project.

When the player jumps, the y direction of the shadow is reversed, so it get's smaller instead of getting bigger.

The problem is, when the blob shadow get's smaller, it get's somehow "concentrated" and darker... i'd rather prefer it to fade out.

Here's a screenshot: screenshot

As you can see, the spot looks harder and darker, when it get's smaller...