Inside the Perimeter and outside it should not share one campaign budget
The client profile, the competing firms and the willingness to drive all change at I-285, so the campaigns should change with them.
Run at least two campaigns. One for the intown market, Midtown, Buckhead, Decatur, Brookhaven and the areas around them. One for the northern suburbs, Sandy Springs, Dunwoody, Roswell, Alpharetta, Johns Creek, Marietta. Add a third only when the first two are funded properly.
Separate campaigns give you separate budgets, and that is the part bid adjustments cannot do. With one campaign, the cheaper geography eats the budget and the expensive one starves, and the report shows a blended number that hides both.
A radius drawn from your office straddles the Perimeter and averages two different markets together. Build the geography from named counties and cities instead, and shape it around the drive you are willing to make.
Write the ad copy separately too. Somebody comparing firms in Alpharetta is weighing a different set of considerations than somebody a mile from your intown office, starting with whether they will ever have to make that drive.