Redevelopment related

My building society in Ghatkopar Mumbai is going for redevelopment. I have a flat measuring 322sq.ft in the building. The developer initially offered additional 20% FSI to all members(24 flats) basis he will be building a 9 floor tower. Later he made a reoffer to the members to provide 36% FSI, subject to approval from BMC/Central Govt, to develop a tower of 20 floors. He has now obtained an approval to develop a tower of 20 floors. In first scenario, I would have got 322+20% = ~385sq.ft and in second scenario, I would be getting 322 + 36% =~440 sq.ft. On both occasions, I had made an interest via our society management committee to buying additional space. According to revised development plan, I am told basic flat size is 450 sq ft and the next is 725 sq. ft. As a result, to purchase a bigger flat, I will have to pay for extra (725-450 = 275sq ft). I am OK with this. However now the developer is saying, I should sell my flat of 450sq.ft and buy the flat of 725 sqft as a separate transaction at a saleable rate he decides. I am keen to know what my entitlements are and appreciate inputs here. Thanks in advance