Depositing an extra time is probably the same effiency loss than just ignoring 1-2 coal in the coal bag ...
That's 1 extra trip every 28 trips, no human player is going to click an extra few time on the bag and conveyor to deposit 1-2 coal -_-
Btw, just make steel bars, way more efficient and better money
And you won't hit the coal GE limit all the time