The volumetric flow rate shown by DWC is the commanded flow rate before pressure advance or nonlinear extrusion is applied. Pressure advance only changes the commanded flow rate during acceleration and deceleration. For the steady speed part of a long move the volumetric flow rate should be the same as the value implied by the GCode command and the nozzle diameter, provided that the actual speed matches the requested speed.
One way to check the calibration of nonlinear extrusion is to use the Duet3D Magnetic Filament Monitor (or the MFM add on to the Roto Tool board) to compare actual vs commanded extrusion during a sequence of long straight moves executed at various speeds and corresponding flow rates.