Exemplary semiconductor processing systems may include a processing chamber and may include a remote plasma unit coupled with the processing chamber. Exemplary systems may also include a mixing manifold coupled between the remote plasma unit and the processing chamber. The mixing manifold can feature a first end and a second end opposite the first end, and can engage the processing chamber at a second end. The mixing manifold can define a central channel through the mixing manifold and can define ports along the exterior of the mixing manifold. The port can be fluidly coupled with a first trench defined within a first end of the mixing manifold. The first trench may be characterized by an inner radius and an outer radius at the first inner sidewall, and the first trench may provide fluid access to the central channel through the first inner sidewall.