I should possibly call them 'projections', because a perspective is something where distances shorten coherently when things are further away, and typically will never have parallel segments to depict things that are parallel in the 3D world. 
And I don't have to make the height of the front face shorter than the width of the same cube. If I do, it will be a stylistic choice of mine. seen on twitter: Really depends on the type of projection you use. You can use foreshortening, but you don't have to, as long as it is consistent between the objects you are using. I mean it's more about the consistency of the general ruleset which is applied. e.g.: I'll have to keep that in mind before setting the pixel sizes into stone tiles.
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