Variation of median axis ratio bias with halo dark matter particle number for (a) 3D and (b) 2D (projection). Axis ratio bias is defined as (q_t−q_m)/q_t where q_t is the true axis ratio and q_m is the measured axis ratio. The bias estimate assuming sampling noise from the MC is shown in green in sub-figure (a) and yellow in sub-figure (b). This is compared with the bias calculated between haloes matched between different resolution FLAMINGO simulations (m₈, m₉ and m₁₀) for both HYDRO (solid lines) and DMO (dashed lines) in the bottom panels of each sub-figure. Δ bias is the difference between the bias estimated with the MC and that from the simulation. The errors for each bin in N were calculated by taking the standard deviation in each bin and dividing by the square root of the number of objects in that bin. For clarity, the 1σ region for the bias from the MC is not plotted here. VR is used for all cases, except the magenta lines which use HBT-HERONS.