The prevailing theory is that its where their face is during their battle pose, as seen by Ridley's height number being about the same as Samus'
As a neutral party, this seems like it would work fine with Sora's traditional fighting pose which does have him hunched quite low (I say this not to confirm Sora but to simply avoid deconfirming him)
But there are other factors involved such as a scaling factor that seems to affect the model as well, and Brave's was scaled down slightly so they might be even shorter than originally thought (like 90% or something like that).
Hope that helps, I really enjoyed following the data stuff so if you have any other questions I can try to answer them too.