If you're using the stock DB, the SW can pick up rather quiet sub contacts beyond 20nm. That gets knocked down a bit with LW/Ami for slow contacts, but will be farther out for fast, noisy contacts.
Either way, you shouldn't have to change the db to get a contact beyond 10nm. Have you tried changing the acoustic conditions? Sounds like you might be in bottom limited sandly littorals at high sea state during a rainstorm if you can't hear something that close.
