To my knowledge, the provisions of Section 18(1) apply the issue -
Section 18 - Common profits, Common expenses and other matters
(1) The common profits of the property shall be distributed among, and the common expenses shall be charged to, the apartment owners according to the percentage of the undivided interest of the apartment owners in the common areas and facilities.
Hence the relevant aspect is the percentage of undivided interest of each apartment owner. Is it equal or otherwise? Provisions of Section 5 inform, as I could understand, that such undivided interest to be proportional to the area of the apartment.
Section 5 - Rights of Apartment Owners
(1) Every person to whom any apartment is sold or otherwise transferred by the promoter shall subject to the other provisions of this Act, be entitled to the exclusive ownership and possession of the apartment so sold or otherwise transferred to him.
(2) Every person who becomes entitled to the exclusive ownership and possession of an apartment shall be entitled to such percentage of undivided interest in the common areas and facilities as may be specified in the Deed of Apartment and such percentage shall be computed by taking, as a basis, the area of the apartment in relation to the aggregate area of all apartments of the building.
(3) (a) The percentage of the undivided interest of each apartment owner in the common areas and facilities shall have a permanent character, and shall not be altered without the written consent of all the apartment owners and approval of the competent authority.
(b) The percentage of the undivided interest in the common areas and facilities shall not be separated from the apartment to which it appertains and shall be deemed to be conveyed or encumbered with apartment, even though such interest is not expressly mentioned in the conveyance or other instrument.
Hence the present arrangement, in view, appears to be fair, just and equitable.