The setting your talking about only is the trigger when launch control works so if you changed the stock setting which you see at 317 MPH to lets say 5 MPH then it would work from 0 to 5 MPH and not above that and as you see the car is at zero MPH at launch so lowering the value would not help.

Either GM did not also include a table with multi values to tweak this condition or LS2edit has not found those tables.