Embodiments of the present invention generally provide apparatus and methods for altering the flow and pressure differential of process gases supplied across a showerhead of a processing chamber to provide improved deposition uniformity across the surface of a substrate disposed therein. In one embodiment, a blocker plate is disposed between a backing plate and a showerhead. In one embodiment, the distance between the blocker plate and the showerhead is adjustable. In another embodiment, the blocker plate has a non-planar surface contour. In another embodiment, a regional blocker plate is disposed between a backing plate and a showerhead. In another embodiment, a central blocker plate and a peripheral blocker plate are disposed between a backing plate and a showerhead.