I see no need to exactly define where the boundaries of these 'passive fields' are. As long as they have one, the 'kinetic energy' reduction would work quite well. If an author NEEDS the "oh holy shit we could fall out of the field" thing for a story, he just does... if not, you just ignore it.
It would also explain how acceleration drive ships can to this insane accelerations with only a little bit fuel. *G*
It would also explain how acceleration drive ships can to this insane accelerations with only a little bit fuel. *G*