Francis,
Acid Copper plating thickness variation will depend on board design.  In
pattern plating different  parts of the pattern carry different current
densities.
If Panel plating the location of the panel affects plating distribution, in
general outside edges of panels carry more cuurrent thant he center.
Some acid copper systems do better than others, but optimizing the plating
cell will pay a lot of dividends.
Best Wishes
George Milad
Global Marketing Manager PWB Metallization
Shipley Ronal Inc