Value of Development Rights in the hand of land owner promoter for discharge of GST under RCM - Goods and Services Tax - GST

In formula prescribed under first proviso to Entry 41A of Notfication 12/2017 - the Revenue vide F.No/354/32/2019 -dated 14/5/2019 has clarified that GST shall b e payable @ 18% on Development rights. What value shall be adapted by the developer towards Value of Development Rights for discharge of liability under RCM? vis a vis the formula ie GST payable on TDR or FSI (including additinal FSI) or both for construction of the project * carpet area of residential apartments / total carpet area of residential and commercial apartment in the project Regards Hubert