Simulated standard deviation of the pairwise fractional difference, σ_Δ(θ), between bright (> 40 mJy) sources separated by different angular scales on the sky, θ. The simulations take the true flux and progressively distort it independently for each pointing with realistic thermal noise, a flux density scale offset, a planar flux density scale gradient and finally residual offsets from the gradient. Here we show the simulations with different distortions both before and after the corresponding corrections are applied to the simulated mosaic catalogues, demonstrating the impact of each corruption and the effectiveness of the refinement procedure. At large separations, σ_Δ(θ) converges to 0.06 in the fully distorted and then corrected case (compared to 0.11 before any correction), whereas on small angular scales it decreases to 0.02.