A few more groups!
Group 5: Americans who on Medicare, Medicaid and VA
Group 6: Americans who qualify and use Indian Health Services formerly under Public Health Services or who have Tribal Health Clinic's that provide health care services.
Group 7: Americans serving in the Amred Forces and their dependents who receive health care through the military. 
Group 8: Americans and non-Americans (primarily migrant workers in mirgrant worker camps) and immigrants who have entered the US illegally in ICE custody, Americans and Non-Americans who live in underserved designated areas or designated institutions who receive direct service care for medical, dental, mental health and preventive health care by the National Health Service Corps. This includes Federally Qualified Health Care Centers and ICE Health Service Corps. 

I do not know the percentage of each group but they should be included in your list of groups. Have no idea #'s of folks who qualify for a group but do not use the services.