Hey @hgbhumkk_4903 When you switch between: Insert & Expand the brush size changes unless the brush in both settings is the same. When you generate a new image and Generative Fill again the brushes go back to their default settings.
After you have pressed Generative Fill, go into Insert and Expand brush and set them to the size, the hardness, and opacity. There is no permentant setting, or none that I am aware of or heard of, unfortunately.