Cost-construct doesn't follow common sense. It follows government negotiated rates for some routes, perhaps some influence from consumer demand, and apparently a bit of good fortune when the cost-construct gods smile on you. I've learned it pays to at least ask.
The R&R point for Caracas, Venezuela is Miami. There's heavy demand for those flights, so prices are generally high. We wanted to cost-construct R&R to Stockholm, Sweden. I asked. The surprising answer was that a flight to Stockholm via Paris on Air France was a little cheaper than going to Miami. Who would think?!? No money out of pocket! Yep, R&R is in Stockholm. :-)