Orleans, Jefferson and St. Tammany are three auctions wearing one metro's name
Parish lines separate the budgets because they separate the buyers, the competitors and the price of a deal.
Draw the targeting on parish and submarket shapes rather than a radius. A circle from an office in the urban core takes in water, a good deal of Lake Pontchartrain and towns you have no inventory in. Polygons around Metairie and Kenner, around the Orleans submarkets you work, and around Mandeville, Covington and Slidell give you budgets you can actually read.
Target by where the building is as well as where the searcher sits. A corporate real estate manager evaluating a Jefferson Parish requirement may be sitting in Houston or Atlanta when they search, and presence targeting alone will hide them from you.
Report by parish from day one. A blended cost per inquiry across three parishes averages a market you are winning with one you are losing and tells you to do nothing about either.
Keep the Northshore funded separately. Clicks there are usually cheaper, which means a shared budget will quietly drift across the lake and starve the campaigns you opened the account for.