Good observations.
I think the smaller venues enable them to better screen who gets in, I don’t think there have been but a few protestors vs. a half-dozen or more disruptions in the big arenas. I also think this is intentional, they set up the “overflow” area where people can hear him but can’t disrupt and draw bad PR. It’s a lot harder to pin the blame on Trump if something happens where he’s not even aware of it happening and doesn’t interact with the disruptor.
Good point. I have noticed that now that you mention it.