Comparison of estimates of the spectrum of convective flows obtained from the synthetic data based on flows from a MURaM simulation. The method of HDS2012 applied to this synthetic data (solid blue line) can be improved by using a scale-dependent signal-to-noise correction (dashed orange line, this work). Both estimates give the correct order of magnitude of the flow (green line), although the estimate from the method of HDS2012 is not a strict upper limit. When the underlying assumptions are improved (solid orange line), our best estimate results in a larger upper limit.