GIMP :: How To Set Radius In Gaussian Blur

I was using the Gaussian Blur around letters to contrast the background and getting a very wide radius with a very gradual but complete shift in intensity from the edge of the blur to the edge of the letters. That is to say, the blur effect would extend all the way out to the Blur radius fading to nothing and the brightest part of the blur was very near the edge of the letters and not far inside the middle of a letter. That was great!!! Exactly what I wanted!

Then I went to do it again and got the default behavior:

No matter how wide I set the radius in the Gaussian Blur it is still the same width, it is just more faded. And the range of the intensity is dramatically reduced, with the brightest part of the blur far inside the edges of the letters, no matter how much I grow the Alpha to Selection of the letters. Now I am very unhappy.

I tried Reset all Filters, but the 2nd behavior is obviously the default. So how did I do that??? How did I get the 1st behavior? How did I get the Gaussian Blur to extend out so much farther without overwhelming the background? The default behavior of a Gaussian Blur of an Alpha to Selection of letters that are substantially grown is that they completely overwhelms the background and there is hardly any gradient, it is just a uniform halo with little change in intensity.