Cosmological constraints attainable for AT2017gfo as a function of the constraints on the ejecta geometry. The uncertainty associated with peculiar velocity modelling dominates for a well-constrained geometry, while a poorly constrained shape would dominate the error-budget when the fractional uncertainty exceeds 5%. The small scatter across the independent datasets from days 1.4–3.4 post-merger (Sneppen et al. 2023) puts an upper bound on the statistical uncertainty on the geometry of a few percent (indicated with grey shading). Additionally, prior line shape constraints (blue shading) suggest percent-precision geometrical constraints may be attainable (Sneppen et al. 2023). Thus, both the EPM consistency and line shape analysis suggest, that AT2017gfo is in the regime where peculiar velocity modelling is the dominant uncertainty.