This is because while 'astitine' isn't an accepted misspelling of 'astatine', it begins with 'a' and 'as', therefore making it acceptable for 'a' and 'as'.
I think I need a new strategy. I went around the world ~1.9 times, first to see which countries started with A, then which countries' capitals, and then time ran out XD I didn't even get to Oceania the second time
I count 10.
AshgAbAt (just all A's)
AntAnAnArivo (all A's until the end!) or
Ant-An-An-Arivo
Hope that's helpful :)