Accuracy is a rating that determines an attack's chance to hit.
It also has a less known quality related to critical hits, where there is an equal chance to avoid critical strikes (but not the entire.
For these critters, size has a lot to do with accuracy.
It makes sense when you figure all the positional calculations are angles and lengths.
The bigger the lengths, or distance between.
Off the backs of some giants, and through some data gathering of my own, i've prepared for you an extensive post on effective accuracy caps for pve, along with the reasons and theories.