Hi cow
I have a 2388 and run one to two large wire concaves in the last or middle position for higher yielding crops of wheat and barley. Usually one in the last position all the time, then as the yields increase add one in the middle position.
As for the key stock grates i run one in the middle position in the grates. I think that this lets the grain out that may be still in the rotor. I run the slotted grates without any bars at all in the first and last position.
This would be for wheat that is yielding 60 - 100 bushells.
This settings really helped decrease my rotor losses.
If yield are low then it have all three slotted grates in all the time, and only one large wire concave in the last position.
Hope this helps
Jimmy