The present disclosure relates to passive flow control devices or FCDs and modeling methods applicable to same. In particular, a new method to extrapolate the value of a reference FRR tool to other tools with the same architecture, but different ratings. Instead of scaling the output of the model, the data of the available characterizations is used to extrapolate what the characterization results would be to the different FRR. This estimated data set is then used to fit a new model for the uncharacterized FRR tool.