An aftertreatment system comprises a SCR system. A mixing assembly is positioned upstream of the SCR system and includes a housing defining a flow path for an exhaust gas. An injection port is defined on a first sidewall of the housing and oriented at a predetermined angle relative to a longitudinal axis of the flow path. A mixer is positioned within the flow path downstream of the injection port and includes a plurality of plates each positioned in the flow path. A first plate is positioned distal to the injection port and adjacent to a second sidewall of the housing opposite to the first sidewall. The first plate has a first length substantially longer than a length of the other plates and extends in a direction upstream of the mixer. An exhaust reductant injector is positioned on the first sidewall of the housing proximal to the injection port.