Modification of reductant (e.g., diesel exhaust fluid, DEF) tank location, for example during vehicle up-fitting may result in less than optimal operation of the DEF system due to inaccurate DEF system calibration. In one example approach, the above issue can be at least partially addressed by adjusting control system parameters for system control and diagnostics based on an input indicative of, or any modification to, the DEF tank location. In this way, DEF tank location flexibility is maintained, while also maintaining emission control and diagnostic accuracy.