Just to clarify, it's only ARC specific in that the locals have to be on the ARC you are getting. If the locals you get are only on the WA, then the guide data won't be on the EA, why would it be? However, if the locals are on both ARC's, then you will get guide data from either one.
Where it gets a little confusing, lets say you get locals from city A on the EA, but your locals are on both ARC's. If you go city B, and use the WA, you will get the guide data for the OTA channels in city B, even though you can not get your locals because of the spotbeam. The key is your locals have to be on the ARC you are using.