The smaller one will be facing you when all the plates are in situ in the basket. Make sure the steel plates all have the bevel facing out and the flat side facing in.
Sorry if I sound dense but...... if I understand you right the smaller one goes into the splined inner part of the cage hub first so that when its got all the other parts in place and you fit it into the outer cage its the one one now outside of the assembly facing you?
Or to put it another way as the outer cage sits on the bike the smaller one goes in last if you can/could fit all the parts that way ?
I think the penny has dropped I've just noticed the special circlip that I suspect is the reason it has the smaller friction plate.
It does not help that the previous owner had obviously had the clutch in bits so I am reluctant to rely on how it was previously assembled as the clutch action was none existent.