User blog comment:DE-Note/What Determines the Strength of One's Aura?/@comment-7622429-20150529163833/@comment-26018514-20150529174326

I don't see it as "quality" so much as training/focus.

Let us use RvB's Basis(Halo) as a comparison;

in Halo Lore, the Spartan armor shields are adapted from the jackal shield technology. There is a huge difference in how hard it is to kill a Spartan as opposed to a jackal, not because of power source, but because of shape.

How this is adapted to Aura:
 * Aura is also an energy field native to all life forms on Remnant, making them harder to damage.
 * In the uninitiated, this aura is diffused throughout the body naturally, meaning internal organs like the heart are just as resistant as the skin to any outside force... however none of them are as resistant as if the entirety was focused in one place.
 * Hunters train to learn how to use this energy for both defense and offense, by focusing what they have on the skin for defense, or externally or overlaying their weapons for offense.