Under a small employer health benefit plan:
(1) the index rate for a class of business may not exceed the index rate for any other class of business by more than 20 percent; and
(2) premium rates charged during a rating period to small employers in a class of business with similar case characteristics for the same or similar coverage, or premium rates that could be charged to those employers under the rating system for that class of business, may not vary from the index rate by more than 25 percent.