Should condo fees be share equally?

I live in a small condominium building with only 10 units. Our monthly expenses cover the same for every unit (insurance, water, trash pickup, ground maintenance, etc.) Some units are smaller than others but the larger units do not affect the costs. In this case, shouldn't the condo fees be shared equally? We previously had this procedure but a new owner who has 2 smaller units reported that it is usual practice to charge by the size of the unit.  Maine