Doesn't matter what RDJ's real height is - he wore lifts for all or most of his scenes next to other actors to look taller than 5'8" - and no amount of calculations from his height to projected assumptions of what that would translate to in armour will affect the final size of the figure. The suited Iron Man armours in the films are meant to be taller than many regular characters. Remember, there's supposed to be a guy inside those suits. I also think the size of the Iron Man characters likely varies quite a bit o screen just due to CGI and cinematic framing. As a virtual image, Iron Man is probably very inconsistent in many ways, including height and size.
I always felt the HT Iron Man figures were rather under-scaled, especially the earlier armours, when displayed against other Marvel/Avengers figures. It's fairly clear when you see them lined up that the illusion of a man, even a 5'10"-ish Tony Stark doesn't fit inside the armour. I don't know, maybe I'm wrong and the Iron Man armours are supposed to be like a Tardis tesseract with more space inside than the outer container.
This Mark 1 should have been bigger. Watch some scenes from the movie and you'll see how it towers over other characters. I don't know just how much bigger it should be, and likely can't calculate it to any degree of accuracy, but it should be bigger in concept.
Does it matter though? This is what we got from HT since the very first Iron Man figure back in 2009 and that's as good as it's going to be. However, this was a missed opportunity to correct the Mark 1 and give us something much better. I feel like HT dropped the ball on the die-cast upgrades to the earlier armours, like Mark 3 (my favourite armour) being a complete mess, and now the Mark 1 falling somewhere into the same abyss of "meh" die-cast upgrades. I suppose it's fine for anyone who missed out on the previous two plastic Mark 1 figures, but for some of us who have one or more of those it seems like this new version is easy to pass on - notwithstanding the price which doesn't seem to draw many of us in to reinvest in this "upgrade". Some of these die-cast versions are merely reissues with major material improvements (the die-cast) and minor superficial improvements (i.e. paint job), but no significant redevelopment, reengineering or upgrade.
