I have been playing it fast and loose for the most part, I do have some general guiding factors on my actions though.
1) Dimitri thinks that alot of Aetherius' problems (Legion, plagues, Urzog) are the fault of Antioch's actions in the past, while it is a terrible thing to do - holding the actions of a people who had no active hand (maybe) in past events - it is still karmic retribution for it.
2) Antioch turned away from Antimagick for a while, and then just suddenly comes back. While that's great, you don't get to ping pong back and forth like that as a political entity and not suffer consequences.
3) Personally, Dimitri cannot make himself help a people who predominantly just do not care. He empathizes with those who are actively trying to do something, but a city should stand on its own two feet.
4) He also is being a bit of a jerk and saying 'look it says no where in our treaty that we have to help you against extraplanar threats.' Yes it is in the spirit of the treaty (which is a little ironic now that i think about it), but if we started going with the spirit of things instead of the letter of things it sets a really irritating precedent down the road