ratio for baffle

[cbdeajr]

I am looking at building a separator lid for a 55 gal barrel with a 6 inch inlet and outlet. However I can not find the ratio for cutting the baffle. Also would it help to install a wall from the input to past where the relief cut starts so as to direct all of the dust to that area. I was thinking that way you could help prevent some of the find dust from making it back to the discharge tube.
Cecil