Good question. As of right now I'm 90% sure that the multiplier works for speed and roll, pitch, and yaw optimal mass however I have not tested out to see if it could effect anything. Possibly the ability to stop or lateral thrusters?
All yo will need to know, and if you dont find it in his videos send him a message, really nice guy always answer any questions i may have. Real shame that the FD dev crew dont watch his stuff or they would nip 70-90% of the problems in the bud before it hits the forums.