On the other hand, his voice is also very American (and so is his personality), which may be why he's hard for you to write.

I think that is it - he's very American (well, very American-TV-character), and what's probably meant to look down-to-earth and human often just comes across as - well, confusing. But he does very much stick to those principles, though. I do wonder what he thought Delenn had done in the war, or who he thought she'd been back on Minbar - surely he'd have asked her more than one question about her parents? But maybe he wouldn't, after all.