Maximum warp amplitude as a function of radius for our four models (top panel), and for a selection of recent estimates for the older population – rather than in Cepheids or other young populations – in the literature (lower panel). Two of these studies looked at the lopsidedness of the warp and in these cases we give both the warp upwards and downwards, indicated by the two lines for Amôres et al. (2017, with the upward warp being the greater) and the uncertainty bar for the Red Giant Branch (RGB) results of Romero-Gómez et al. (2019, with the downward warp being the greater value).