Check "not initially created" on the encounter or set max respawn and total respawn to 0.
Normal diff count is the number of AI present at the start, but you let it respawn another one.
Edited by game user10 on Apr 25, 2013 at 05:34 AM

If these are for a Single Player Map:
For the Encounters: change nothing but the name and the 3d firing flag (if they are flying ai) make sure respawn enabled is Not checked.
For the Squads: Make sure they have a name and an actor type, if β represents the number of ai you want to spawn (should be equal to the starting locations you have placed) make sure the squads are set up like this:

normal diff count: β
insane diff count: β
respawn min actors: β
respawn max actors: β
respawn total: β
respawn delay: 1 to: 1 seconds

If α represents what you named the encounter and γ represents what you named the squad you can spawn the encounter with the command:

ai_place α/γ

This works in console for sapien and ingame, this will also work in scripts.
If you set them to respawn they will spawn on top of eachother as you mentioned.
This command does not apply for multiplayer: The AI will not sync in multiplayer period.