I believe this works similar to how abjurations work on zilart mobs such as the ones in sky and also ground kings.
on those they have 2 pools of 100% chance, and one of 18% chance, this is then split 25% per abjuration. Kirin is odd because he only has 3 abjurations and as such, 25% of both the 100% pool and the 18% pool are blank, that gives kirin 88.5% chance of an abjuration instead of 118% on any of the other mobs.
I believe the hide droprate on Behemoth/KB is similar to this, with the 1st pool of 100% chance and the 2nd at 64% with TH4 but the blank amount being 10%
this would give 90% on the first pool with TH being irellevant, and then 57.6% chance on the 2nd pool with TH4 (64*0.9)
that gives 147.6% chance of a hide
this would give 140.4% chance with TH2 which is bang on
Axelution
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3 years ago 
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Let's start with Byakko https://www.youtube.com/watch?v=Dh8EtckP2hs video from 2005 showing 2 hides can drop(thanks Falaras) http://www.ffxidb.com/zones/130/byakko this fits with 2 chances of 18% each with TH4 from the uncommon category for the hides (36% total with TH4)
Behemoth and King Behemoth, 0 dropping is possible
but so is 2 as evidenced by the drop rate on both on ffxidb
http://www.ffxidb.com/zones/127/behemoth
http://www.ffxidb.com/zones/127/king-behemoth
I believe this works similar to how abjurations work on zilart mobs such as the ones in sky and also ground kings. on those they have 2 pools of 100% chance, and one of 18% chance, this is then split 25% per abjuration. Kirin is odd because he only has 3 abjurations and as such, 25% of both the 100% pool and the 18% pool are blank, that gives kirin 88.5% chance of an abjuration instead of 118% on any of the other mobs.
I believe the hide droprate on Behemoth/KB is similar to this, with the 1st pool of 100% chance and the 2nd at 64% with TH4 but the blank amount being 10% this would give 90% on the first pool with TH being irellevant, and then 57.6% chance on the 2nd pool with TH4 (64*0.9) that gives 147.6% chance of a hide
this would give 140.4% chance with TH2 which is bang on