Well, first thing to bind is the Spoilers Axis command to Joystick R-AXIS Z.
Then bind the SET AUTO SPOILERS ARMING to Joystick Button 28.
After that, open the sensitivity and start with extreme deadzone at 50%. This will flatten both the bottom left and top right corner lines. The target is, when you place your spoiler lever at the first detent, you want the white dot of the sensitivity curve to be flat on the bottom. But we don’t want the top right corner to be flat. To do that, adjust the neutral point and sensitivity so that you can move the curve to the right, reducing the flat line at the top right as small as possible, while maintaining the bottom left flat line to stay at the bottom when your spoiler is at the first detent. In the end, the extreme deadzone might be lower than 50%.
Once this done, you should have no spoiler movement between UP and first detent, while the first detent will arm auto-spoilers and disarm them as soon as you move the spoilers elsewhere. And your spoilers will move slowly from the first detent all the way down to fully deploy. You have to do this testing while in the aircraft to make it easier. Adjust the sliders, see how it works, then adjust again until you’re happy with it.