Pixel-pixel matrix χ² values of the first 400 of the 143 GHz FFP8 simulations, evaluated against 18-arbitrary-eigenmode fits to either the first 50, 83, or 200 simulations. The χ² of the simulation data set used to compute the pixel-pixel covariance matrix has been normalized here. Due to the limited number of simulations, the real variance, estimated from the simulations that were not used to compute the pixel-pixel matrix, is significantly higher (i.e., the red line jumps at about 50, the green line at about 83, and the blue line at about 200).