I've done a few extra steps than I needed. Basically when baking the texture out I didn't have to mess with the environment. The diffuse coefficient doesn't include any bounce light or light for that matter!
When I say the Concrete texture looks better, look at the chin, they are close to each other in UV space hence looking half decent. Sewing the halves together will create a seamless look but you would struggle with the rear of the head!
I think the only way would be to make sure the rear edges use the lower/max limits of UV space.
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