Interesting it is not shown on the charts but 20+ years ago I acquired a suntour freewheel with an 11 tooth high cog. It would only screw into a special 13 tooth 2nd position cog but I managed to modify it to work with a 12 tooth second cog for an 11-17 strait block. It was my secret weapon for downhill wind driven time trialing back before 11 tooth cassettes were available. Once got 2nd place using it at tour of Gila TT which has a long fast downhill, even beat John Fry in that race and he held the national 40Km record.