I'm trying to book a one-way *A award XXX-ORD-SNA/LAX-AKL, with a < 24 hour layover in LA. United tells me no can do, I cannot fly into SNA and out of LAX. Why? I realize neither stopovers nor surface segments are allowed, but I don't think this is either. They insisted that I book XXX-ORD-LAX/LAX-AKL instead. Seems to me there are a couple of issues here:

1) Both UA and NZ (the overwater carrier) publish routings XXX-AKL; neither uses MPM. ORD is not on the NZ routing, so that cannot possibly apply. The UA routing includes CHI and LAX.

2) SNA and LAX are co-terminals for UA, so should be interchangeable as far as routing rules go, right? (Although admittedly not part of a multi-airport city like WAS or CHI.)

Am I misunderstanding how co-terminals work? I've done this before for EWR/JFK, which are also not part of a multi-airport city (I believe NYC = JFK/LGA), but not on a *A award.

Yes, I realize I can try calling back until I get an agent who will do it, but I'm curious whether our local experts believe it should actually be allowed---I had assumed it would be.