Spherically averaged 21 cm PSs at z = 10.8 corresponding to a parameter vector in our test set, θ_mock. Pink points and error bars correspond to a mock ∼2256 h observation with HERA (see text for details). In orange, we plot different realisations, varying ICs at a fixed θ_mock, but spherically averaging the 2D PS down to μ_min = 0, as is commonly done when forward-modelling. In blue, we plot these realisations but instead averaging only down to μ_min = 0.97 to account for the HERA footprint in cylindrical space (see red line in Figure 2). Excising low μ modes removes the bias seen in the orange curves, but dramatically increases the sample variance. The dashed black line corresponds to the output of 21cmPSDenoiser from a single 2D PS realisation, averaged down to μ_min = 0.97. We see that applying 21cmPSDenoiser mitigates both the bias and the sample variance.