Rera carpet area v/s mofa carpet exploited by builder to charge more

I had made a booking for a flat in Mumbai in the year 2014 based on super built up area in the MOFA era. The project was delayed and the possession is now to be handed over in Apr 2021. I had not registered the agreement until now. In the meanwhile the project came under the scope of the RERA. The builder has now tactfully used a clause in RERA wherein he has used the definition of carpet area in RERA v/s that of MOFA to claim an additional amount (for exactly the same super built up area as was before) and hence asking me for increased cost. In effect, a same flat handed over to a MOFA agreement holder (one who registered agreement in 2015) does not include this additional amount. Does this classify as fraud and is he rightful in charging me so?