Yeah, but a) normal human height has probably adjusted upwards a bit over the 550 years between now and the Fall of Reach, and b) the IVs are going to be big on average anyway, since they're selected for (among other things) athleticism.
Also, didn't Blur actually say that they deliberately exaggerated his height in that last scene? They'd know.
See above. I know the IIs are all crazy tall, but it's like 6-10 inches taller than the IVs, not a foot and a half
Whether or not it was deliberate it matches what is know in canon.