Simple as this, in Halo 3, elites bow their heads. In Reach, then stand on their tip toes.
BTW, you logic about things growing in different gravity really doesn't make sense. First, the only reason why we can't live on an Earth with a higher gravity is than our odies wouldn't be able to withstand the presur and we would be squashed by the air.
To disprove you: If the less impact gravity has on something, the bigger it gets, then when I go under water a few feet, I should grow a couple inches due to lower gravity, but if I swam down a mile (bear with me), I would much smaller than I actually am because water pressure would simulate that higher effect of gravity. The reason why i used water is becase it can create an effect that is very much like gravity in space., but when you go deeper it is like being in the surface of Jupiter)