Abstract: An apparatus (100) and method are provided for polishing a substrate (105) that achieves a high-planarization uniformity. In one embodiment, the apparatus (100) includes a subcarrier (165) with a lower surface (170), a flexible member (245) extending across the lower surface, and a control-insert (280) disposed between the flexible member and the lower surface. The flexible member (245) has a surface adapted to press the substrate against a polishing pad. The control-insert (280) inhibits non-planar polishing by providing a variable removal rate across the substrate surface. The control-insert (245) can be an annular ring (280A) located near an outer edge of the flexible member (245) to control the removal rate near an edge of the substrate (105), or a disk (280B) near a center (290) of the flexible member to control the removal rate near a center of the substrate. The removal rate can be further controlled by varying a cross-sectional thickness of the control-insert (245).