I'm thinking they'll either look at a slightly bigger plant than...

I'm thinking they'll either look at a slightly bigger plant than the 1.8mtpa scoping study plant and keep the mining rate the same (more ore, less waste) which would increase the CAPEX but also likely lead to an increased NPV. Otherwise keep the plant size the same at the same through-put and the China Pit starter pit mine life would increase from 13 years but these additional years wouldn't have a significant impact on NPV, the decreased strip ration would though.
I'd have no issue if they decided to get a bit more aggressive in regard to the initial plant size - even double it to ~3.5mtpa. The resource is there, they've previously said they'll likely start underground mining at around year 7 so why not pre-load more of the CAPEX and offset by an increased initial production rate. All indicators are that finance will be straightforward and as it is MYL's share of the CAPEX is only US$97m at a scoping study level + contingencies, finance costs etc etc which is relatively low for a new mine.