when using the loader, it puts the back skin over the right thigh skin.
Perhaps I'm missing something or misunderstanding you, because the same effect seems occurs in the vanilla game. When the girl leans as far back as possible, the glare patch on her right buttock will disappear from view. It's just how the game layers are laid out.
The back skin is influenced by a Mask. Normally, that Mask will "airbrush out" the bottom edge of the back skin so that it blends in with the hip and buttock. But this means that if a modder draws something on the BACK layer (such as a set of angel wings), their drawing will
also get airbrushes out as it approaches the girl's hips. Therefore the Loader gives users the ability to retain the original Mask, or replace it with a modified one.
If you're unhappy with the appearance of the girl's body (or the mods that you've applied to it) then you can try adjusting the
fixBackMask parameter in
Settings.txt. You'll need to restart the game in order for the change to take effect.