Responsibility for condo contributions is based upon unit factors assigned by the developer when the condo plan is registered.
Unit factors are frequently based upon floor area. Still, other considerations may include potential sales price, location in the complex (higher floors are worth more in an apartment), availability to exclusive use common areas etc.
Today most developers have to be pretty open to the formulae used. However, it can be tough to find out about older complexes.
In my experience, ½ of the owners think their unit factors are too high, and half think others are too low. 😊