How much will retirees have to pay for insurance? (II)

Why seven tiers?

According to the Illinois State Universities Annuitants Association (SUAA):

As sited [sic] from a memo to Rep. Tom Cross from CMS which is to be a part of the record this
Amendment allows:

• the Director of CMS to set the premiums that are paid by retirees in the Group Health Insurance Program every year.   
• the proposed retiree contributions will pay a percentage of their healthcare costs on a sliding scale. The scale is based on (1) length of service, and (2) ability to pay.   
• the percentage of cost the retiree will pay will also be based on his or her pension level. Pension amounts will be broken up into seven tiers; the higher the tier, the more the retiree will pay.  
• retirees who are eligible for Medicare (generally 65 years old and above) cost the state substantially less than those who are not on Medicare. Since the contributions will be based on paying a percent of the cost of care for the state, those retirees on Medicare will pay significantly less than those (generally younger and still working) who are not.  
• those who have already retired when this plan goes into effect will pay based on their ability to pay, but will be given service credit at the highest level. However, regardless of the contribution amount determined under those rules, the new plan contribution will not be less for any retiree than the amount they contribute under the current policy.

Why seven tiers?