and while you do have a point, the clean grain pan overfilling will also increase tailings, and should be your indicator of overloading the machine.  there actually shouldn't be but two conditions while harvesting corn that there ever should be a condition where there are overloaded sieves.

in a perfect threshing environment all that would really be needed is the center chaffer section.  the rest of the chaffer is superfluous, but we don't always run in a perfect world and hence the need for more cleaning area.

I don't like setting the extension as wide because some of the MOG has to be walked out, cob chips specifically, and while the air blast will kinda float the chips over the center section, there is not enough air to do the extension too, so some MOG will drop into through the extension straight into the tailings.

opening the extension also bleeds some air away from the center section.

here is something to think about,.....why do some combine operators have to replace the cleaning system bushings pretty regularly while others have almost no trouble???????