Several female action figure bodies such as CG and TTL bodies have a pronounced gap below the rib cage. This looks as if the figure is sucking in its belly and is particularly visible under tight stretchy clothes.
Here's a simple way to improve its looks.
Reduce the gap between the torso and the hip section by using a piece of soft thin foam rubber (2mm thick) sized 70x20mm. Cut the top edge to match the curve of the rib cage.
Cutting the lower and side edges in a taper (beveled) will make the outline of the foam even less visible.
Under tight clothes the foam should remain in place without the need to attach it to the body.
The result can be seen in this picture of Gemma.
With Fleur I went a bit further and also added padding to her waist and hips to reduce the wasp-waist effect of the CG body.
After padding the gap below her rib cage, I added a second layer of 2mm thin foam (sized 70x40mm) on top of that, making the foam stretch all across the front and sides.
The second layer of foam extends from the chest all the way down to the lower sides of the hip section.
Finally I made a sleeve out of a piece (80x40mm) of pale orange lycra to cover and retain the layers of foam.