It is almost impossible to concentrate roach on the deck as they will come up and down in the water column to feed. In order to give myself a chance of catching them at every level I use a strung out shotting pattern which slows the fall of the hookbait. More often than not, the fish are sat in the bottom half of the water column so I have the shot slightly closer the further up the rig I go. This gets it through the top layer a little quicker but gives any lingering fish a chance.
The further up the rig, the less the gap is between shot The last shot should sit just above the hooklength