An adaptive feedback control method is provided for a chemical mechanical polish process to minimize a dielectric layer clearing time difference between two annular regions on a substrate. An optical system with an optical window passes below the polishing pad and detects reflected light interference signals from at least two annular regions. A pre-clearing time difference is determined and is used to calculate an adjustment to one or both of a CMP head membrane pressure and a retaining ring pressure. The pressure adjustment is applied before the end of the polish cycle to avoid the need for a second polish cycle and to reduce a dishing difference and a resistance difference in a metal layer in the at least two annular regions. In some embodiments, a second pressure adjustment is performed before the end of the cycle and different CMP head membrane pressure adjustments are made in different pressure zones.