There is no east / west separation in regards to which arc a customer is set up for. What I mean is, just because someone is west of the Mississippi River, for example, doesn't mean they will be on the western arc (or maybe they will be). My locals (Dayton OH) are on western arc. Cincinnati locals (~40 miles due south) are on eastern arc and Columbus locals (~60 miles due east) are also on eastern arc.
That said, on the west coast, I'm 99% certain those customers are in fact on the western arc as it's physically difficult to "see" the eastern arc satellites due to the distance and curvature of the earth. It's not impossible though as a short-lived satellite service called Voom had their (single) satellite at 61.5º.
