What is the reference for subclust function?

The subclust function in Matlab use multiple radius parameter radii in their algorithm. I know that Matlab already stated two references for subclust function in their website. (Chiu, S. "Fuzzy Model Identification Based on Cluster Estimation" and Yager, R. and D. Filev, "Generation of Fuzzy Rules by Mountain Clustering"), but these references only use single radius originally.

Is there any references that improve the substractive clustering algorithm, so it can use multiple radius? Or they just implement it in Matlab by themselves?