Well, you can (with most kites) cut the rearlines fully (infinite sheeting), and the kite will still "fly" very well, fully depowered of course, and not possible to steer the kite.
You can not steer/turn the kite, not even with rear lines if too much depower stroke and bar pushed out - here every single individual kite and size got its own limit.
Thus not possible to give you a number, WHERE the depower goes into the "grey zone" where control is lost....
If you name a specific kite and size, some can give their input to where they find the sheeting should stop on this particular model
Regarding the OR Stick Shift bar, it has an option to trim the rear lines too, apart from the adjustable front line sheeting - thus it might give you 120 cm in total when everything is added together.
This does not mean your kite can work at all, when depowered so much - probably not....