An apparatus for processing a substrate, comprising: a process chamber having a track; a carrier connected to the track; upper and lower proximity heads in the chamber and positioned along the path, the proximity heads having opposing faces that define a gap in which a meniscus of fluid is formed, the path being defined along the gap between the opposing faces; a first pre-wet dispenser and a second pre-wet dispenser disposed along side of the upper proximity head and directed toward the path; a drive for moving each of the pre-wet dispensers between a center position along the length of the upper proximity head and opposite outer positions near outer ends of the upper proximity head; and a pre-wet controller for causing the drive to move each of the first and second pre-wet dispensers based on a position of the carrier when moved under the first and second pre-wet dispensers.