A device is provided for controlling fluid flow over a window of a movable optical instrument housing. The device includes a generally annular body having an inner peripheral edge configured to correspond to a peripheral edge of the window of the housing and an outer peripheral edge, an arcuate outer surface disposed between the inner peripheral edge and the outer peripheral edge, and a reduced width portion between the inner peripheral edge and the outer peripheral edge. The reduced width portion is configured to lower elevation torque. Other embodiments of the device and methods for controlling fluid flow are further disclosed.