It's a trick question, Calimshan was destroyed in the spell plague, there are no cities in Calimshan because it no longer exists, the nation collapsed after the effects of the second era of skyfire. If it did still exist than Memnon, Calimport and Manshaka would be the major cities.
I noticed the same thing. The first couple times I did the skirmish during the event period I received 1,000 AD. Then I received 650 AD, then I received 400 AD. Every time when I opened the chest it said 1,000 AD were inside even when I received less. Either it's bugged or there is diminishing rewards that is not indicated…