Question about DefenseFollow

I don't seem to be getting all of the +Def value from some items. My defense is 478 while I equip fetish of the fallen. However, when I equip force of will, wich gives +10 def, my total defense goes up to 482, not 488 as I expected. Can anyone shed some light on this? Thanks in advance.

For a level 70 : 2.36 Defense Rating = 2 41/112 Defense Rating = 1 Defense Skill