how about a complete guess without really understanding how things are set up..
1. I think it creates a higher resonance factor giving the illusion of more bass
2. the area under the desk creates a additional order over the DB band pass design that boosts a narrow frequency band
3. sweet!!!! my first 8" Db was a flop and one day will have a go at it again with a 8" dvc sub I recently acquired for under my desk