You're using your own experience of the games you've played to base your judgment on. The games I ran with 12 players were marathon games of 6-12 hours, so everyone got the spotlight and they were equally engaged. The breaking down into squads was to make running combat manageable.

Over the years I've run for many larger groups, the largest being 20 people playing CP2020 for 8 hours. Man, I can't do that anymore. Upon reflection I think I did an adequate job, but I'd like to think that over the past 20 years my skills have markedly improved and now I find my sweet spot is 3-4 players to provide the kind of gaming experience I want to provide.

You're using your own experience of the games you've played to base your judgment on. The games I ran with 12 players were marathon games of 6-12 hours, so everyone got the spotlight and they were equally engaged. The breaking down into squads was to make running combat manageable.

Over the years I've run for many larger groups, the largest being 20 people playing CP2020 for 8 hours. Man, I can't do that anymore. Upon reflection I think I did an adequate job, but I'd like to think that over the past 20 years my skills have markedly improved and now I find my sweet spot is 3-4 players to provide the kind of gaming experience I want to provide.

I couldn't do it anymore either. It's for younger folks or people with a lot more energy than I can manage.

Larger groups work better for me in Narrative style games. I have run Star Trek for 10 players and One Ring for 11 players with no problems. D&D 3.5,

I draw the line at 5 players maximum.

It's unusual to have people just get up and do other stuff. Seems like it's possible because they only see combat as any sort of challenge, and if it's social, they are not down for it.

I also have to inject here that I have diabetes, and sometimes i need to get up and walk around. I try and play that out in a game as my character pacing and thinking, but I am definitely still involved in what is going on in the game, and stay in character, even if it is "Pacing and stretching in character"

The "NPCs react as if they are getting blown off" is a neat perception. Going to write that down.

Normally though after a session like this, I'd contact the player privately and ask "what's the deal are you bored?"

Also, I have a daughter that's got ADD, she often does stuff like this, Doesn't make her bad. Similarly, have had players that have Bipolar disorder, but still played as well as they could manage, but when they were really Manic, is was really tough, because they'd argue and come up with things that didn't make sense to anyone else in the group.

Perhaps a talk is in order. They have a need you might not be filling to keep them interested and motivated. Maybe find some of the various player styles articles around the net or in D&D 3.5. those helped me out a lot in making the gaming stew out of diverse ingredients (players)