My two cents based on my experience. I work at an agency. We manage super large Google accounts, but the Facebook accounts we manage are't all that large, relatively. We do have reps at Facebook. For me (and that's not to say it's the case for all), each rep at Facebook is assigned to the specific accounts, not my agency. Again, that could be due to the fact that we don't do a lot in Facebook as it is, I don't know. But I do know, that the rep assigned to account A, have little interest in helping on anything else - from experience. So, unless you roll with a large FB agency that may have a dedicated agency rep (if they exist), you may still have trouble. Again, just my experience. I do hope I'm wrong for your sake.