Contrast computed for each line. The neutral contrast C=l is highlighted by the dotted lines. Middle: contrast estimation across the SOPHIE to SPIRou wavelength range. Right: histogram of contrast values for SOPHIE and SPIRou. Top: contrast averaged in wavelength bins for SOPHIE and SPIRou, computed using a geometric mean to capture the proportional nature of the per-line contrast (e.g., the geometric mean ${\overline{C}}_{\text{geo}}={\left({\displaystyle {\prod }_{i=1}^N{C}_i}\right)}^{1/N}$ equals 1 for opposite contrasts, such as C = 0.5 and C = 2). The bar heights are proportional to the expected RV amplitude, while their color encodes the phase of the signal.