The game is quite fun but I think that it can get slow at the end with few players: aAgents are spread across the globe and a part of your turn is just to get near an agent to attack him.
This variant tries to "solve this problem" in a very simple way. It cannot be played withe the Mission Expansion.
You'll need pawns to represent "closed cities".
> Whenever an agent is killed, the player owning the agent chooses an empty city and close it by putting a pawn on it.
1. The first player who loses an agent chooses the city he closes.
2. Subsequents players must choose a city connected to a closed city.
In subsequent turns :
* an asset cannot be placed on a closed city, re-roll the dice until you obtain an avelable city.
* an agent cannot cross an closed city.
Progressively, the map is going to be smaller...