That was a very good point you made rubberduck,and thats the main advantage about those hybrid combines like the CTS or the Lexion(threshing cylinder in front of the rotors),the rotors can take over a part of the threshing process and support the cylinder in front,AND separate the grain much better with their higher centrifugal forces caused by the smaller diameter of the rotors.And the threshing cylinder supports together with the beater drums the feeding process into the rotors.Thats the reason why they shine in small grains,especially when it gets tough,a skilled operator is required though,knowing the "secrets" how to set up a machine like that.And as mentioned before by rubberduck,use your precleaner,open it wide enough and speed the fan up,and then feed the whole system as much as the engine is able to handle.
When Deere released the CTS concept(long before Claas came out with the Lexion),its main purpose was rice,and a combine that shines in rice should be able to able to handle a wide range of conditions.You will run circles around a 2188 during the late hours,when it gets tough,which is not uncommon in the canadian praries,those single rotor combines(the STS included) just suck in those conditions.