That's exactly right. I don't know that much of Sync besides what is told in the anime, but I can easily think of another example: Kanda Yu (DGM). Those that know a little of his personality, know that he keeps his distance, hates a lot, likes it when you leave him alone, and is angry 99% of the time when in company. And thoughe prides himself in being one of the strongest exorcists of the Order (with right and reason), he also has that side where he respects those that deserve it (his mentor, Marie (who's one of his closest friends), Allen, Komui, Lenalee, "Lavi").
It takes a while to get through Kanda. First of all, there's his emotional barrier and second SPOILER HERE.
What I mean to say, is for Kanda to fall in love (he's more than capable of it, he's got a big heart inside his armour) a)you need to give him time, let him grow closer to his love-interest, b) accept that [see spoiler], scars heal slowly, c)not annoy the heck out of him, d) not compete with him, e) I'm quoting Hoshino concerning that person on this one:x
So yeah, keeping that in mind, I get a headache from people who put him with an Allen/Lavi-like character. Kanda's got a short fuse and is emotionally quite unstable. Give him a solid rock to depend on. :V
And yes, I probably thought way too much about this. |D; RP'ing is a good way of doing that.
What I probably want to say, though, is that character analysis is important if you want to make things work.