It varies day by day, these are just my experiences. And how I run my sets. New birds on cold days we like I like to run about 4dz floaters, 1 or 2dz shells along the bank or a sandbar depending on how much room you have to set them. If it's warm and we aren't seeing a whole lot we run less. I like to run a slightly bigger spread then what I'm seeing in the flocks flying if we don't have a lot in the area.
With stale birds, a few floaters I mean like 1-4 will work wonders. With just simple calling single clucks usually will pull the birds with shot in their but like your hunting over a silage pile.
Just try different things. I always like to bring extra decoys cause its easy enough to just throw them back in the blind if it's not working right.