There were two things I didn't know about GIMP when I first followed this tutorial, which was written for another GIMP from another millenia even. One thing was that this tutorial could be scripted. The other thing was that it had been scripted already.
Ever since my Photoshop friend dumped me, I rarely have the need to make a floating logo like I did in the last century, but the recommended levels setting in that tutorial is still a good magical default for many of my image making needs.
download
Download this and other scripts.
Instead of showing the pertinent piece of the code, I decided to show via screenshot of what this layer effect managed to do to Adrians tatertots.
It works better for turning your blurred mask into a bloated and sharper mask.