I had thought of doing something similar to that Lee in an attempt to salvage TERRIBLE data. Had really nice red and blue data but green was bad due to the auto guider going on the fritz. Wanted to use PixelMath and mask the green FWHM with the red and turn lines into fainter dots
Didn't work so well but what you've done sounds good. As for the lower FWHM, what you have done is increased the central region with the poor data which has increased the "half maximum". You've created an artificial cone