RE:RE:RE:RE:RE:RE:Carats per tonI don't think you're missing anything because the grade (cpht) of south lobe is lower anyway.
Looking back at the 2017 outlook the make this point :- "The overall grades of the south lobe are lower than the centre and north lobes resulting in lower diamond production, which is expected."
However that shouldn't affect the value/ton since those fewer stones are more valuable.
Dividing the forecast $170,000,000 by 270,000 stones gives $629 per carat and I don't think that's any different from where it's been so far (excluding specials).