the definition of progress variable in FGM model
 

I want to model a combustor using FGM model in Fluent-19.2. I found the definition of progress(Yc) is not clear in the model settings.
In ansys-19.2, the FGM table could be generated using chemkin-19.2, and in chemkin, the definition of Yc (the coefficients of each speices ) could be modified by users, but this definition is not contiuned in the final outputed table files. So I am not sure if it consistant with the defintion in fluent. otherwise, is it possible to modify the definition of Yc in Fluent solver?