I've been wondering lately about the types of South Park's creators. From watching a few interviews, I am pretty confident that Matt Stone is an SeFi. He has locked-on eyes, syncopated momentum, blunt/monotone articulation, and tension in his cheeks. I am less sure about Trey Parker. I haven't been able to find as much quality footage of him, but my guess is NeTi. He also has syncopated momentum, but has more naive eyes, makes Si scowls, and lacks any sign of blunt or monotone articulation. I am not too sure, though.
I can see what you're talking about. Also, I've noticed that his voice does tend to swell. All deeper voices tend to sound monotone to me. In this case, it was a superficial impression. I just needed to listen more carefully.
I have watched more video of Trey Parker, and I am now seeing Fe>Ti and Si>Ne. I also think that he might be a J-lead (FeSi), but I'm not yet sure.