I failed to understant this design... What did I miss?

It lets you have filtered chests, think like a sorting system. Point the proxy at the destination chest (where you want to store stuff). The poxy block will have a black square on the face where it expects to have the destination chest. on a different face tap it with a diamond (it won't consume it). Add storage touching that face and then fill the slots with 1 of each item you want in the destination. If you leave an empty slot then that is considered open and anything can fill that space. Use an inventory connector on the proxy block to connect it to the system.

From what I can tell the proxies have a higher priority than the storage connector so it will try to fill the proxy storages before adding items to the generic storage

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So just by using chests as the "filter" inventory, they don't actually seem to work. I've filled the chest with the items I want to filter, but other items are still able to enter into the "destination" chest. Anyone have any advice on this? Is there a specific storage block I need to use?

EDIT: The chests need to be the same size. I assumed it was filtering only based on the filter chest, but it is telling the items where to go in the destination chest as well