@arma473 @Jip , yeah the suggestion was based off of mapgen maps having no real hints at how much reclaim is on the map. Didn't even taken into account adaptive maps, and how unit reclaim is generated.
My initial thought was just port ozone values. Taking a look, I didn't realise how far off some of these values are. Maybe it'll be simpler just to have part of the vault description dedicated to reclaim values and allow map makers to manually input initial figures, giving a ballpark figure for mass.