The best way to test it is to set them to passive then approach an enemy without attacking it, preferably without even being spotted. Your companion will probably open fire before you even break stealth, which is not how 'passive' is supposed to work. They're supposed to wait until you attack.
No matter if I set it to "Aggressive, or Passive"(Yes I have tried and tested both for a extensive amount), Boone does what he wants to do.
Imagine going down deep into one of those vaults with ED-E and Boone. You trying searching the rooms systematically, but you are doomed to fail. Just right when you begin searching, your hear that stupid Trumpet song coming out of ED-E speakers, and Boone spatting out "You won't get away this time". :toughninja:
So what do you do? You go follow them and kill what every got their attention and get back to the same room and continue searching, right? WRONG!
The moment you get back in the first room you were in the same [censored] will happen again, and again, until you get lost in the vault, and can't remember where that first room was. So you are force to search rooms randomly. :facepalm:
Your only alternative is the leave the companions somewhere, but then whats the point in having them? Beside you want ED-E to tag along cause he opens up quests and story when you complete certain quests or speak to certain people.