I think you misunderstand the purpose behind the 80% requirement. It means of all the money the insurance companies take in from premium payments from customers they must spend 80% of it on healthcare. It isnt judged on individual use of ones healthcare insurance, its judged on the total healthcare operating costs of the company for the year compared to their total income via premiums.
It basically removes your fear of increased costs from your insurance company, because unless they are legitimately facing increased costs due from the medical service provider side of things their increased premium costs will be returned to the customer each year.
For example if you had 100 people in an insurance pool and the company was charging each person 100/mo(10k/mo coming in total) and their operational costs for healthcare were 8k/mo... if the company decided to raise premiums to 120/mo they would have to have seen their healthcare costs increase as well(to 9.6k/mo), if they dont then the extra money they charge will have to be returned to the customer at the end of the year in the form of a rebate.