@Viters
I agree to an extent, the breasts are certainly effecting judgement, but that top half is still too tall IMHO.  I've never seen a real woman proportioned like that and I can't imagine how many naked women I've seen thanks to the web.  His figure looks almost the proportions she would be if she were in high heels, I think she looks way to tall, and I'm trying to make him realise that it's not the overall height that is making her look tall, it's the proportions inbetween, from the top of her head to the base of her feet.

He needs an arse kicking for being idle if he doesn't try what I said (even if he doesn't like the result).

Basically, he should prioritise 'eyeballing' the proportions over any guidelines.  If he's obsessed with this height thing, then all he has to do, after reducing the height of the top half of the torso, is elongate another part/parts.  He has the head, neck, top and bottom part of the torso, the thighs, and the shins to play around with and balance-up if he's really that obsessed with keeping the height the same as it is now.

And height is relative anyway.

But yup, I think the top half of that torso is definitely too tall for a girl of that build, I've never seen a real woman with those proportions, I don't care what the recognised drawing guides say.  I've seen women who aren't too far off that, but they're very rare and aren't what I'd call blueprint material for a nice female form.  I suppose if I could sum it up as basically as possible; she looks ok but she's a bit too extreme to look natural.

Here's a girl in high-heels, she looks natural, but the thing to note here is that Diamond gives-off the same proportional look even without high heels :