I've heard of that as well, but at the time of this estimation, we were working with the assumption that both ships are going to be quite similar, but of course built at different shipyards.
As to how we estimated the design costs, we looked at comparator vessels that we selected and what the design costs were for them—in particular, the AOPS. We made adjustments for capability and the light ship weight, for instance.
That would be how we arrived at our estimates.