AD Banners - How to Use with Multiple countries

Currently (If I have this right) we can select a global effect for banners or choose by country.

This seems to cause some problems in loading many banners plus have them not showing correctly for example, for example lets say I have

Australia
United States
United Kingdom

and then the global settings, Currently I need to load banners in global and to the country say Australia, so if the select aus they will see the aus banners but the global keep going as well ?

If i just set the countries and the user has not selected a country (and views global) the banners will not show (if i just added them to a particular country) so my question is why can we not have it so that we can add banners to selected countries, then if no country / location is selected in geo then all banners show regardless of country ?

/ So that it works in exactly the same way as listings do now, if you go to the site and no country is selected then all listings show, if you select a country then those listings show

is this possible if so how ?