I have run Meetup hackfests for more than 12 people (running Savage Tide). In fact, I personally like doing it. But it's not the same experience at all. It's like comparing apples and oranges.
If you go into a game with 12 people expecting the same experience as a game with 4-6, you're going to be very disappointed. You have to go into it expecting a lot of out of game chatter, introducing yourself to other people and making general hobby small talk while observing the battle that unfolds. You have to expect and enjoy a wargame atmosphere. Would I give it up for a 4-6 player table? Absolutely not. But do I feel uncomfortable running it? Absolutely not.