Best-fit model of the spectrum at the position of GQ Lup B. Top: observed spectrum (black), joint best-fit model (green) and components of the starlight model and companion (blue and brown, respectively). Centre: data with the best-fit starlight model subtracted compared to the companion model. Bottom: residuals of the best-fit model. The shaded region represents the root-squared diagonal of the covariance matrix with the optimal noise scaling factor.