The leak detection filter in the fill tool flood-fill method can cause
gaps between filled areas and boundary strokes. This is undesirable, so
the boundary stroke radius is scaled by half for drawing, typically
creating enough overlap between boundaries and the generated fill
strokes to hide artifacts. This behavior is copied from GPv2.
Pull Request: https://projects.blender.org/blender/blender/pulls/122307
aa88ced5c2