Factory Flow Simulation - Buffer Capacity based on sizes

Hello.

I would like assistance in how you could simulate the following behaviour: 

There is a storage location that holds two kinds of Parts. Large Parts and Small Parts. It can store twice the number of Small Parts than Large Parts. For example. It could store 5 Large Parts. Or 10 Small Parts. Or 2 Large Parts and 6 Small Parts, etc. Or 4 Large Parts and 2 Small Parts and so on. Editing the Capacity of the Storage with Resource Configuration does not capture my use case since it doesn't consider the 'size' of the Part in storage - every Part is treated as occupying the same amount of capacity. 

In getting this behaviour to work I explored using the User Logic and User Attributes. But If there are other ways to achieve my functionality I would like to hear them. 

My thinking was to assign a weighting of 1 to the Small Parts and a weighting of 2 to the Large Parts with the User Attributes. Within the User Logic of the Storage I want to "sum" the Storage Capacity using these weightings to check if the Storage has exceeded its capacity.

EG: If it has in Storage, 2 Small Parts and 1 Large Parts its current capacity being consumed is 4 [(2*1)+(1*2) = 4]

Any Assistance and guidance on how to achieve this is appreciated.

Thank you.