Don't rely on F on regional CX - it's liable to disappear randomly through equipment changes or it simply being pulled from the route.

I assume this is in the northern winter so you can't go to ANC.

LHR-SFO-MIA is 155 miles longer than LHR-LAX-MIA.

DFW-SJU-JFK is 2219 miles better than DFW-ORD-JFK