Sorry for the almost tl;dr, needed some examples here. but…
I haven’t seen any posts confirming this for sure, but I was attacking different types of mobs while grinding and realized something. I was using 2h spear, which has a base aoe ratio of 4. I was fighting mainly medium/large mobs, and with the combo of them, I was able to hit 3 medium, 2 medium 1 large, and 2 large. These results were the same even when there were more monsters in range, ex 2 medium 2 large, and it always seemed to prioritize hitting the large size monsters first.
For another example I was fighting small size monsters, and when there were 4 of these together, I was actually able to hit 4 at once with autos, but when they were mixed in with any medium monsters I was only able to hit 3.
To the point, based on this, perhaps aoe ratio is a characteristic of every attack, and is reduced by enemies at the rate of 1 per small monster, 1.5 for medium monster, and 2 for large monsters, and prioritizes targets in order from large > medium > small. And as a rule, if after minusing from a larger target, you still have any amount > 0, you will still hit another target as per priority order, taken down until you reach 0 or less.
As per the examples, with an aoe ratio of 4 for auto attacks.
2 large = 2 + 2 = 4
2 medium 1 large = 2 + 1.5 + 1.5 = 5
3 medium = 1.5 + 1.5 + 1.5 = 4
2 medium 1 small = 1.5 + 1.5 + 1 = 4
4 small = 1 + 1 + 1 + 1 = 4
My only downfall since I started into the 2nd half of this beta test, is that I only have a cata to test with, so I have no aoe ratio weapons that add additional stuff ( no rares ) or 2handed swords with the bonus aoe ratio. Is there anyone who could possibly test out other numbers to see if this is true and verify with other aoe ratios?