Storage capacity : how is it calculated ?

Day 5,264, 14:26 Published in Belgium Republic of Moldova by Jeiry

Hello everyone !

I'm probably not the only one, but my storage capacity had recently been overwhelmed, probably due to the excess of "Daily Challenge" rewards.

So I took a look at my storage and... I discovered that I have no clue how the maximum capacity is calculated !
I thought it was simply the addition of the "Final products" and the "Raw materials" items (which is what the Wiki says by the way), but it's not at all what happens in my storage. Adding my items just gets me to 164.669 while my storage says that my surplus is "480.470/473.000" ! What ? Can you help me understanding that ?

Secondary question :
As I'm in surplus, I cannot sell items on the marketplace (didn't know that rule until yesterday). Neither can I find a way to simply ditch items. Is there any way to get rid of some of my items (other than increasing the storage capacity) ?

Thanks.