Hey there, so after some searching and testing I had to go with the move the slot 10 armor to slot 3, there doesn't seem to be a way to move the slot visually so I will just have to live with it in between the hand and armor slots.
Couple issues though. First off the option to hide optimize from sub classes seems to have broke at some point. Now when I change a sub class it is telling me it's optimizing equipment. The enable on sub class is set to false.
The other issue which seems like it may be a pain. So with the armor slot changed to id 3 it is optimizing properly, ie. it stays in it's slot when optimizing on class change and from the optimize in the equip window it always works perfectly.
There were some class changes however that the slot was removing the item. After a lot of testing I finally figured out when it's happening. If the class has a 2 handed weapon equipped and then changes to a dual wield class it removes the slot 3 armor. This happens whether there is a shield in the offhand or not. Also none of my dual wield classes have the ability to equip 2 handers, not sure if that's important.