Phew. Just spent 5 minutes banging my head against this editing wall. More and more, FTPro is annoying me. I try to fill in the Adriatic, and I just end up making the Appenino taller. If I enter a value and try to paint the selection to that elevation (i.e., rather than raising or lowering terrain, simply entering "50" feet and trying to paint the terrain to that elevation), nothing happens. Filling in basins doesn't work.
Then I decided to go nuts and just try raising/lowering terrain, and putting in a value of "100" resulted in filling in 8000 ft-deep oceans with one sweep, and knocking 1500-ft tall hills into 1000-ft deep ocean with one sweep.
How the heck to people actually edit landforms in FTPro?