decompressed items are smaller than compressed items

Hey all.

Wondering if anyone has seen this behaviour and has a explanation (or ideally reference KB or something). In the past couple of years, I have seen a few customers who have EV reporting that the decompressed size of an item is substantially smaller than the compressed size.  IIRC it is not uncommon for EV to report double the size of compressed items in a Vault Store than the decompressed size. Some isolated investigation has shown that the EV VSDB is showing the correct data when extracting and looking at the actual items, but we did not dig into why or how this counter-intuitive evidence is the way it is.

Anyone have a great explanation for this?

Just to be clear, I am talking about actual item sizes, not involving storage level compression or SiSing.

TIA for any feedback on this perplexing topic.