Ratio between the azimuthal noise profile in the Q_ϕ image and in the cADI-reduced image; both images come from the same observations. The asymptotic value (black line) of in the readout-noise (RON) limited region comes from the fact that only half the frames are used to obtain the Stokes Q image (respectively Stokes U) when the HWP has a position angle of 0° and 45° (respectively22.5° and 67.5°). The sensitivity is higher in the Q_ϕ image compared to the cADI image in the blue-shaded area below 1.28′′.