The feathering slider belongs to the refinement block. It takes the ‘average’ of what is currently selected, and analyses contents (not AI, but pretty effective). It’s not just a ‘gradient inside’. Look at this one (image credit: found on the internet, sorry):
It’s a pretty rough selection over the dragon. Without refinement:
- it does not cover all of the dragon
- it covers the sky visible through the statue.
With refinement, the selection is extended to other parts of the dragon:
Increasing the radius: the sky gets excluded!
Adjusting the opacity and contrast of the mask:
With a more carefully drawn mask and perhaps more, smaller masks, and involving parameters (to avoid bleeding over to the grass), the result could be further improved.