A tailings conveyance (98) including a housing (100) having a front plate (112), a back plate (114), and a wall (110), and is adapted to recycle tailings (80) through a cleaning system (26) of a combine using at least one impeller (104,104A). The wall (110) of the housing (100) describes an arc near the impeller paddles (106) over a segment of a circle described by the circumference of the impeller (104,104A). The wall (110) further continues on a tangent away from the circle at a point of tangency (118). A sensor (150) is positioned proximate to the point of tangency (118), and senses whether a space between the front plate (112) and the back plate (114) directly adjacent to the sensor (150) is obscured by tailings (80) as the impeller (104,104A) rotates. A controller or control system connected to the sensor (150) calculates an amount or percentage of time the space between the front plate (112) and the back plate (114) directly adjacent to the sensor (150) is obscured by tailings (80) as the impeller (104,104A) rotates.
