Mrs. and I are planning a trip EWR-PNI-NRT-EWR in a few years. When sampling prices, after selecting J for the first two segments, the complete trip is in the $6k to $7k when flying NRT-EWR in J, but is over $15k if flying the last leg in W.
Airfare structure is something that even the best FTers haven't been able to decode.