Any time you break a county in your AA, you are asking for additional scrutiny.
This is a pretty broad statement. I work with hundreds of small banks and know of numerous ones that have part of a county, but not all of it in their AA. Why? There's are dozen's of reasons. Such as, the county:
Is divided by a geographical limitation (mountain, river without quick bridge access, etc.)
Has a city on one side and is rural on the other. The bank sits on the far rural side and doesn't try to meet the needs of the urban area. (very common in my area).
The city is large and the bank has one location on one side of the city. They don't serve the whole city - nor want to.
I could go on and on, but I think you get the idea. Mel mentioned some legitimate reasons and has rights to be concerned about the criticism.