Legendary Kinetic Sphere (Orb) has Force Absorption (Enhancement) +20%, but seems to apply 15% on the +tab.

Character has 0% when equipping it.

logs:
(Effects): You benefit from your Legendary Kinetic Sphere.
(Effects): --- Enhancement modifier to Force Damage Vulnerability: +10,085%


The same process with: Band of Diani ir'Wynarn returns


+tab
from 0%
to 21%

(Effects): You benefit from your Band of Diani ir'Wynarn.
(Effects): --- Enhancement modifier to Light Damage Vulnerability: +10,079%


Adding The Zarash'ak Ward to the mix.

(Effects): You have multiple effects granting an Enhancement bonus to Force Damage Vulnerability that do not stack. ( Legendary Kinetic Sphere and The Zarash'ak Ward )
(Effects): --- Enhancement modifier to Force Damage Vulnerability: +10,085%


Ok, looks like some pattern after all x__X