Hi Sean,
Could you post a screenshot of the decal viewer of that model. Maybe you have overlapping areas or other strange things. Or sending your model to me could also help me find out what goes wrong for you.
BTW, for the head you should also take a look at the options 'Opacity falloff' (paint opacity decreases for parts of the model that face away from the camera), 'Front and Back Side' (paint both front and back-facing parts of the model or not) and 'Only paint visible pixels' (only apply paint to parts of model that are visible).
This will be solved using the 'Opacity falloff'. Without this option turned on, the paint you apply in front view would also fall on the sides of the model (and thus be stretched out over there). You can see an illustration of the effect of 'Opacity falloff' on page 24 of the manual.
As mentioned in the manual, the option to auto-decal the model is only available if the application is launched using the A:M plugin. The reason is that 3DPainter can then instruct A:M to add the stamps etc...
Best regards,
Filip