Hi, did you ever get to the bottom of this?
I would suspect that with the AFF, since inline dedupe, compression and compaction are on by default, you are just seeing the result of all the efficiency savings. The output of DF -S would give you most of the the answer. For the compaction you will need to look at the Aggregate level Storage Efficiency output using the privilege advanced command aggr show-efficiency. Hopefully all those figures add up.
Hope it helps,