I set a MAX RANGE DEAD BAND to about +10%. At throttle calibration in the game (notepad) I set the idle, notch and ramp positions. The reverse button (or handle position in my case HOTAS THURSTMASTER WARTHOG) is mapped to reduce Power Axis 1/2. Also set Trottle Hardware has Reverse.
Now reverse works properly.
You may set a bigger or smaller dead band, but depending on you hardware the reverse may not engage, disengage, no go full reverse or even return to idle asymetrically.
