So not sure I fully understand...what columns are you joining on? is it Year_Month and Location?
If so there is no location BLO in Table 1. If I choose a full outer join you can hopefully see what is going on
It might be that this might be what you need...in that SUM(Cost Value)/SUM(NetWeight*QTY) with CustomerSegment in the Level of Detail (Column Shelf) will give you the result you want, but that might just be a bit of a fluke due to the limited 2 rows of data you've posted here.