If a person wants SMP for density to existing hair would you use bigger darker dots than someone who is bald?

Scalp MicroPigmentation is basically a tattoo.  Just like any tattoo, the final result depend on the artist performing the procedure.  The size of the dots matter and but the technique and the pigment used will also matter.  If you want bigger dots, just visit any tattoo artist.Your SMP faded because the SMP usually requires several repeat sessions. 

Hello, and thank you for your question.
SMP, or scalp micropigmentation, is a painless procedure that uses highly specialized equipment and unique techniques to carefully and expertly inject all-natural, color-tailored pigments into the scalp creating a completely natural look of the patient’s hairline. A typical procedure involves an initial consultation and two pigmentation sessions to achieve the desired results. You can wash your head the fourth day after the treatment and, during that time, avoid any strenuous activity that will prompt undesired sweating. Once the procedure is complete, the results of a Scalp Micropigmentation treatment can last up to five years. 
In your case, I wouldn't recommend "bigger dots," since that may look unnatural relative to the rest of your hair. Rather, if you wanted more density, another round of SMP would probably be the solution to your problem. 

Gary Linkov, MD
Hair Specialist
Manhattan

Most of our SMP patients return to the office within a few weeks to a few months for a second procedure that can best replicate the ideal density.  I suggest that you have a further fill in, and make sure it is performed by a doctor and his office who have experience with these cases.