Auuuugh
Torment the sleep deprived mind at your peril with your bumping of a missed topic that forces me to log in again just as I log out to close my bloodshot eyes...
Just kidding, but I did miss this somehow and feel I must throw my 2 creds in, I'm sure someone else would but as they haven't then let me muddify the waters for you
The way I've always played it is two kinds of 'gravity' drives.
"Ya, da puny wimpy we can't PUMP YOU UP ones found in da vehicles like da fairy-raft."
Sorry about that, I thought he was busy being governor or something
Anyway he's basically right, vehicle gravity lifters are a weaker smaller cheaper type of device that only works in the presence of a significant gravity field. They are useless on very small worlds (less than 1?) or beyond low orbit. This makes them pretty useless for most orbital operations and all deep space operations, without adding suitable secondary thrusters.
The other type of 'gravity' drive is the much larger and power hungry Maneuver Drive, aka Thruster plate that is found in true spacecraft. These work by manipulating gravity in a totally different way and the performance rating is not based on local gravity but is limited to a maximum of 6 gees.
Anyway, that's my take on it, for what you find it worth, based largely on canon.
Good night all
<yawn>