Exemplary 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 may be characterized by a first end and a second end opposite the first end, and may be coupled with the processing chamber at the second end. The mixing manifold may define a central channel through the mixing manifold, and may define a port along an exterior of the mixing manifold. The port may be fluidly coupled with a first trench defined within the first end of the mixing manifold. The first trench may be characterized by an inner radius at a first inner sidewall and an outer radius, and the first trench may provide fluid access to the central channel through the first inner sidewall.