I too have a "hot spot" in the rear, over the heating element & the top on mine in back seems to get the hotest. I especially noticed it after smoking sausage recently. I would suggest rotating & shuffling your food around to avoid overcooking in areas. I need to get to the "mod's" that have been posted on here.
That tile layed over the chip box snug to the corner is a really quick fix that makes a lot of difference it that corner. Ron turned me onto it and I have kept it in ever since. Simple cheap and effective.
To answer your original question, I don't think it really matters. I would probably put the brisket on the bottom rack and the ribs on the upper racks. Then... when I pulled the ribs... I'd slip the brisket up to the top rack. Don't have a reason for doin it this way... just the way I'd do it.