Well,for at home,folks like the butts on top,to drip and baste the packers.
To me,at comps,I'm more concerned that the packer cooks correct,so I put them on the rack they like and the butts can go anywhere.
The butts tend to drip more,and we cook brisket fat down,so we don't like all the drip on the presentation side of the brisket.
I guess that means,I'd have to spread each enough to not drip on each other,or just let the briskets drip down on the butts.
Sorry,I couldn't be more exact.