Hi guys and gals,
I am encountering a specific problem with the back of the robot :
I fused the part of the back which protrudes from the top, since there is no separation between this part and the whole solid piece which constitutes the torso (commercial life size toy shown below)

Since the torso piece is subdivided with the Subsurf modifier, this additional part has to be too (my model shown below)
Of course, i know have to achieve the squared and pinched cornes, such as shown in the first image.

Adding other edge loops would ruin the overall shape of the subsurfed torso, so it seems to me that the only solution left is the creases.
You can see the result in the image below. It is ugly as hell 🙁 🙁 :(.

Does anyone have an idea on how to proceed to have the squared/pinched corners without the ugly shading artifact ?