Ships in orbit within the AOI get the bonus. The problem is it's difficult to get them on planets close enough to be in the AOI of all of the military bases (whether you use 16 or 24).
Just as a note, the orbiting bonus is technically 25% to attack, although there is a hidden omnipresent bonus (in and out of orbit) to all ships of 1% defense and 1% attack, which stacks additively with the above. So if you had a ship in orbit, but not within the AOI, with 4 nightmare torpedoes (100 attack) you'd actually have 126 attack.
