Theoretical reconstruction error according to the formalism developed in Sect. 3. The stellar distribution is drawn from realisations of the BMG for pointing coordinates to ℓ = 180°,b = 45°. Top: value of the ⟨ r²f/ (1 + f)² ⟩ parameter as a function of apparent i(AB) magnitude. Middle: reconstruction error as a function of the apparent magnitude i(AB) of the stars in the stack and as a function of the complex ellipticity components e₁ or e₂ (colour code). Bottom: reconstruction error on the PSF size. The red line indicates typical requirements for stage IV experiments.