Baking part of model - not full model.

So I'm having an issue where I want to bake the normal map of  part of my model. I've included the high/low prefix for the parts that I'd like baked and left the other parts without naming prefix's. Substance still produces artifcats on the parts that I want left alone. Why is this? See the artifacts on the edge of the coat in the image I've attached. Theres no high poly mesh to bake onto this so why is it producing these results?