SubDing the figure isn't going to fix a rigging/mesh creasing problem like that. It's just going to be a smoother too high shoulder/chest crease. Post it with the clone brush in an image editor or resculpt that area a little on the welded mesh. Moving that region down, tweaking, and smooth brushing in zbrush (or any other modeler with decent sculpting tools) solves that problem. You basically want to fix how the deltoid joins with the pectoral. Of course it helps from the get go if your using a wm or jcm fixed version of the figure. You'll probably want to go with some kind of prefab fix, many people can't be bothered to resculpt things on their own. Maybe the morph tool could help.

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