Part of the issue is that we do not know how it is supposed to work. Looking at it logically I think (note that this is my opinion only) that it should work this way.
  1. Players that joins before the icon turns to Fight can be assigned to a city whether that player is on line or not at the time the assignment is made.
  2. Once the icon turns to Fight, players that have been assigned will be on that city's fight, even if they are not on line.
  3. Any player that enters the fight that has not been assigned, either because did not join or the Host or Vice-Hosts did not assign them, are randomly assigned to a city's fight.
  4. When attacking, all players that enter the fight start at A.
  5. When defending:
    1. Players that enter the fight before the first round starts can garrison on any fort, camp, or the city being defended (B thought G). If they do not garrison before the first round starts they start at G.
    2. Players that have joined but have not entered the fight before the first round starts are assigned to G. This includes players that are not on line.
    3. Players that had not joined and enter the fight after the first round starts are assigned to G.