It seems that even with them set on passive, as soon as they spot an enemy they attack or is it that they attack as soon as we're spotted, so sneak attacks would'nt be an option anyway. I should point out that I have Boon and E-DE, is it that those two in particular attack sooner?

No, all companions are like that. The difference is in non-Passive, they'll attack upon any detection, but in Passive, they won't until you attack or you're being attacked...or, if you're sneaking, as soon as the [ HIDDEN ] turns red and says [ CAUTION ] they'll attack. They're just trying to protect ya. If you want to sneak crit I think it needs to be done while in HIDDEN anyway, once it's red you just get normal crits, but I could be wrong about that, someone can correct me if I am.

It can be very annoying in vaults/indoors tho, because walls/doors are in their way so they'll go rushing up & down stairs/corners to get to enemies their perception can sense.

Only solution is to make them "wait" outside while you explore those areas...they'll still be there when you exit. For more casual use you can tell them to wait a small distance away while you're sneaking, and then if you get into trouble you can run back towards them and they'll cover your retreat.

I think they're attacking on being detected. I'll take your advice and ask them to wait more often. When it comes to sneaking I've noticed that Boon crouches but does E-DE become harder to detect too, as he's up in the air, it's a bit pointless if he's still easy to spot in sneak mode?

Not sure about ED-E....but I do know that companions ability to sneak is typically based on their sneak skill, just like your character. Thus Arcade Gannon is not a very good sneaker, and he constantly tells you so. >.>

Boone has sneak as a Tagged skill so it rises as he/you level. Cass has the same skill-set/tags as Boone. Lily the nightkin is a good sneaker even tho she stays standing. The rest aren't "good" at it. (edit)I'd guess ED-E has no sneak ability at all but I dont know what that does to your chr's detection. Most likely they'd see/attack ED-E while not being able to initially see you.

thanks.

ED-E is generally favorable for snipers has his sensor perk can pick up enemies from great distances. If you could see them through a scope they'll show up on radar.