Configurations - base flange

I don't use sheet metal very often.  Can'tI addconfigurations to a base flange feature?  I want (2)flanges,same profile. extruded (2) diff. lengths.  When Iadded aconfiguration, I expected to get the configuration optionsbelowthe base flange feature menu - however nothing showed up (asitdoes with a reg. extruded feature)SolidworksSheet Metal