So I accidentally came across this nugget of information that I never really put any thought into before, but totally makes sense and may be common knowledge to some or most of you.
When the guys move around the map all together in one group, they talk about everything to each other much more than when people are moving around individually or in smaller groups.
It came across my attention when a guy I was in a game with was complaining about the characters because he said they never talked. I disagreed with him and said these guys were awesome because of the amount of dialogue they had. I then said they talk to each other all the time and realized that was what it was - in my very first game I had played, we all stuck together throughout the entire map because everything was brand new. The other guy said that in his game everyone split up.
I'm sure a lot of you know that they talk more like this, but it was kind of a revelation to me when I realized it, and am enjoying it a lot more now when I can get in a game where everyone moves together. The characters really come alive in that case and it's not just throwaway comments about ammo or weapons, they're talking to and about each other. Such a cool little thing.