A separate budget keeps the market visible
A shared UAE budget often flows to the largest or most responsive audience. That audience may not be in Abu Dhabi. Your Abu Dhabi offer then gets a small sample that cannot support a decision.
For example, a campaign with AED 2,000 for the whole UAE may spend AED 1,500 on Dubai visitors. Abu Dhabi receives AED 500, which is too little to compare two landing pages.
Your brief can set a fixed amount for Abu Dhabi alone. This works because the spend stays in the market you want to test, and the result answers a clear question about that market.