One way to do this would be to create a custom group, put your EB in it, sprinkle in some other Bosses, to make a group of about five, then set that as your ambush.
The drawbacks are, you can't control who's selected out of the group, so you might not get the EB, or you could even get two or more copies of him! The more other Bosses the less likely you'll duplicated your EB, but if you put in too many it will become too random that he will appear.
Plus, an encounter with an EB and three or four Bosses is likely to be too tough for just about anyone to handle. Lts or minions can't be used because they would appear INSTEAD of the EB if your difficulty is not at max. (And you're in a large group)
I know of no other way other than to just set your spawn to Back and hope for the best. Try using a smaller map, so Back spawn points are closer to each other.
Also, make sure you HAVE another "Back" on your map. If you're placing lots of objects, make sure your Boss and his linked EB are the first things you enter in the mission. That way if you have any collections or something set for "Any" they won't grab up the Back slots and force your EB to spawn in the middle.
I basically ran into exactly this problem while developing a mission for one of my story arcs.
The concept for the mission was that the hero was sitting around in his/her SG base doing "monitor duty", but while there, Freakshow hired by his SG's mysterious archenemy start showing up and assault the SG base.
I had started with the idea that the mission would start completely empty of mobs, but there would be a "monitor computer" glowy that the player would click, then this would trigger a series of Freak ambushes, each set to trigger off of the previous ambush being wiped out, then the final ambush would include an AV/EB, and killing the AV/EB would complete the mission.
When I started implementing this mission I found that this idea didn't seem possible at all; I wasn't able to use the death of an ambush as a trigger event for another mission detail, and there's no good way to put an AV/EB in an ambush. I did end up finding a workaround that kind of works for me, which is:
Collection 1
- No trigger
- Nav tool hint: "Watch monitor" (required objective)
- One wall item placed in back of mission
Boss 1
- Triggered by Collection 1 completed
- Nav tool hint: "Defeat intruders" (required objective)
- Freakshow boss placed in front of mission
Ally 1
- Triggered by Boss 1 completed
- Nav tool hint: "Link up with Ally 1" (required objective)
- Ally 1 placed in front of mission with Freakshow guards
Ally 2
- Triggered by Ally 1 completed
- Nav tool hint: "Link up with Ally 2" (required objective)
- Ally 2 placed in front of mission with Freakshow guards
Boss 2
- Triggered by Ally 2 completed
- Nav tool hint: "Defeat Clamor" (required objective)
- Clamor AV/EB placed in front of mission
None of these are "real" ambushes but they do end up spawning Freaks all over the map, along with some allies showing up in response to "intruder alert" alarms to help you out. Sometimes Freaks spawn directly on your head, but sometimes they spawn in a different room; as a result, I too was worried about the player having to hunt all over for the enemies. I solved this by using a "Tiny" abandoned office map for my mission, so you never have to go very far before you find them. A tiny map worked for my story concept, but it might or might not for your story idea, of course.
Hope that helps. If you want to see the above script in action, it is mission 3 of story arc 67335, "Teen Phalanx Forever!"
@PW - Police Woman (50 AR/dev blaster on Liberty)
TALOS - PW war journal - alternate contact tree using MA story arcs
=VICE= "Give me Liberty, or give me debt!"
My recommendation would be to try to find a map with only 2 "back" spawn points that happen to be in the same room. I don't know for sure that one exists, but that'd be your best shot, I think.
One thing you can do is create a test arc, with exactly the number of bosses in it as there are "back" spawn points, then run through on a character with stealth to see where they all are. Yes, this is tedious, but it's worth it if you can manage to create the effect you want.
I wish the maps just had little dots on them telling you where the spawn points were up-front.
And for a while things were cold,
They were scared down in their holes
The forest that once was green
Was colored black by those killing machines
Okay, I'm pretty much relegated to the idea that what I am trying to do is likely not available at the moment, but I'm putting this out there on the chance someone has a trick to help me (or maybe just has seen what I cannot seem to).
Final mission and I intend to trigger an EB after the boss is defeated. Preferably, the EB spawns in the same final room as the boss for the obvious reason that having to search for him spoils the flow. Although the EB is set to spawn in "back" of the map (same as the boss), he tends to spawn closer to the middle of the map. Even if it is technically the back of the map, it's defnitely a ways away from the last room. I had hoped I could correct this by having the EB appear in an ambush, but ambush teams do not appear to be customizable. So, am I missing something or do I just have to make do? Also, if there is an alternative that will address my "get thee into the last room, EB" problem, I would appreciate hearing it.
Chill.
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50's: Jennifer Halloween, DM/DA Scrapper; Black Peet, 50 DM/WP Brute; Siansha, Soldier; Miss Terie, Elec/Dark Corrupter