Comparison between marginal posterior distributions for the magnetic field strength computed by solving the same inversion problem as in Fig. 1, under model M₁ and using a uniform prior over the full range of plasma density values ρ_i ∈ [10⁻¹³, 10⁻¹¹] kg m⁻¹ and then marginalising (solid-line), taking a cut of the two-dimensional joint posterior at the value μ_ρi = 1.9 × 10⁻¹² kg m⁻¹ (dashed line), and solving the problem using a Gaussian prior with μ_ρi = 1.9 × 10⁻¹² kg m⁻¹ and σ_ρi = 0.5μ_ρi (dotted line).