How can my condo fee be more expensive than other owners?

I just bought a condo 6 months ago. There is a $200 a month condo fee and only three condos here. In the past we divided everything equally and my dues were raised by an attorney to $420 and the other owners were raised to $330 We are the condo board  I dont see how she can tell us to pay more because we have the larger unit? This covers lawn maintenance, insurance and snowplowing.