Lower risk people are enrolled all the time in THE HEATH CARE INDUSTRY at the same price as everyone else. where I work, a 26 year old male pays the same as a 30 year old female, or a 52 year old man.
A family of 3 pays the same as a Catholic family of 7. It's called cost averaging
As an employer that has provided health insurance to my employees for over 20 years, where we have shopped the market usually on average every 2 years, I have NEVER seen a quote from an insurance company that didn't include a breakdown of premiums based on the people insured. Now your company may average costs in terms of what their employees have taken out of their paychecks, such that all employees pay the same amount or same percentage of their gross, but that comes from your employer not the insurance company.
Now usually when it comes to these rates the insurance company usually charges a family rate for more than 2 dependents...hence for a family of a husband, spouse and 2 children, the rate is the same if there are more children. This is actually based on actuarial data that shows that additional children don't really significantly add to the risk.