OK further update.
Played a 3player, 6 team game (Yellow/Grey/Green (yes green)/Orange/Red/Purple) and we cruised through with no team re-rolls required. It was actually to easy in the end and we found that a lot of the time teams sat inactive as they werent close enough to the entry points to contribute that much.
Lost 2 Space Marines but got 1 back with the resupply card, so comfortable win for the Marines but it was good to finish without getting creamed. Maybe for these bigger games there should be more than 4 entry points for the Stealers...maybe a fifth would make it more interesting. Then again it was our first larger game.
Has anyone else found this with the 6 team games ?
No, indeed in my experience it's been exactly the opposite. My group doesn't play 3-player nearly as often as 2- or 4- player, but when we've tried it we've found we always do better with an even number of players. Better than 75% win record in 2- and 4- player, and lost every single 3-player game we've ever tried. So if you felt your first 3-player game was a cakewalk, I'd expect that it was just a case of getting a lucky draw on the event cards.
Are you certain you were using the 3-player void lock card? 1 out of every 3 event cards should result in 2 different locations getting 5 genestealers each. That should rarely feel "easy". One failed attack roll (or two major spawns on the same location drawn back to back) and the automatic marine death cycle starts grinding. In my experience 3-player games tend to start off strong, but then somewhere along the line there's a critical turn after which everything tanks.
Also three thoughts pop into my head when I read where you wrote "teams sat inactive", especially when you say that you had marines out of range to contribute yet felt the game was too easy. So I ask:
1) Was the green team one of the frequently inactive ones?
2) Just to be sure, you are playing cards for those "inactive" teams, right? Just choosing not to take any actions when the cards resolve. I'm trying to picture how a team would "sit inactive" and half the time it'd be at least placing a support token somewhere. So that "inactive" phrasing kinda raises a flag for me (as in, it makes me wonder if you've got all the rules right), unless what you really meant was just some fire teams hardly ever played attack cards.
3) How did people take it when they had to "sit inactive" and couldn't make a useful play? We have one person we play with from time to time that feels the need to always have an effective turn. To the point where if the best thing they could do is to sit still and wait while others deal with the current threat, they'll instead interfere with somebody else's obvious moves just so they can make a single attack themselves with their least potent marine, or disrupt the whole formation and prevent attacks just so they can personally put a token on a door. It's a weird sort of self-centered short sightedness. Needless to say, we don't tend to win much when that person is playing.
3-player games are usually pretty tough, yours might have been a lucky fluke.