One of the things I always have trouble explaining at the workshops is a topic in Proportion that deals with heads high. Mostly, I just can't draw on white boards, at all, and this topic is pretty diagram heavy.
Here are two models (from Persona 4) who represent the height difference between two average humans. This diagram is mostly to show the technical difference between heads-high and height. Someone can be 8 heads high and 5 feet, or 6 feet. This catalogues the differences between them, as well as the differences between a broad character, and a slender one, as a bonus.
Not that this diagram should not be taken at face value and used for stock for the following reasons:
1) Shorter people tend to have fewer heads high. Though the point of this is to try to illustrate that height and heads high have nothing to do with each other, there's still a correlation in real life. This can get hard to realistically depict in a comic, where the reader expects more consistency, or at least definable differences.
2) 8 heads is a 'heroic figure', often seen in comics. The slender figure looks to have a small head compared to the buffer character. The higher the heads, the wider the figure tends to have to be to offset this. Of course, a smaller head can be aesthetic, too - it depends on the look one wants.
3) You don't have to force everyone in your character roster to be the same heads-high, though it seems this is usually the case. 70's anime often had one or two characters that broke the mold of the rest of the cast - usually comedic, or humongous guys [link]
A real human is generally only 6 heads. Realistic portrayals tend to be 7. Most eastern and western comics are 8, because this cuts the figure more memorably - But some anime are 9 or more, like Fist of the North Star and Sailor Moon mangas.
4) [I'm aware these aren't cannon outfits or anything - I was trying to keep it simple while still suggesting where clothes would cut, too.]
5) There are a few issues I ran into while mapping these two characters to exactly 8 heads. While this is the traditional breakdown, I find the knees set too low for my tastes, and similarly the elbows also feel too low - Generally in anime/manga at least, extra height is given at the shins and forearms, rather than the thighs and tops of the arms, which I suspect is usually how that goes in real life. I think this has a lot to do with foreshortening and perspective, when drawing the characters at anything other than straight on - The knee to the shin, when looking down at some one will look even smaller, so it pays to exaggerate.
As a side note to the heads-high discussion, it's interesting to note how much a single foot of difference can make to the area that a person takes up. Naoto could probably fit right through the neck of Kanji's shirt without even any exaggeration. I've been nearly hit in the face with an elbow myself while walking behind someone that much taller. This kind of stuff is really interesting to try to depict in a believable way in illustrations. Most of the time, a height difference like this has to be mollified because it just looks too weird.
As another observational note, sometimes people as tall as Kanji (especially at his age, where he's taller than anyone around) tend to hunch over the way he often is shown to do in game. I've even had trouble hearing two tall people talk to each other over my head! There's a lot of reasons to start hunching over more and more without even realizing it...