Hello Khan,
When I set the StackSize for example for the "High External Stone Gate" to 10 in the "Large Wooden Box" but the StackSize in StackModifier is 1 then Stacking will not work. If I set the Stacksize in StackModifier to 2 then stacking to 10 works in the Box.
This works with any item i have tryied.
Seems like an item that has a StackSize of 1 (in StackModifier) cannot be stacked higher in a container regardless from any setting in StackItemStorage.
Regards,
Michael