I did this for GA planes. My left throttle controls all throttles and right one I use for Mixture. Here is how I set it up. I use the slider on the stick for the propeller axis as well.
You want to reassign the left axis to “THROTTLE AXIS” and the right one to “MIXTURE AXIS (0 to 100%)”. The throttle sliders have buttons inside them at each indent, so when you are assigning the axis, make sure it says “Joystick L-Axis X” etc and not “BUTTON xxxx”. I wiggle the axis between reverse and FLX indent, I had to try a few times.
Mixture all the way forward is 100% rich. Here is my sensitivity setting and assignment. You have to lock the reverse lever as this setting will use full 100% of the slider including reverse area.
You’ll notice that the sensitivity setting for the Mixture is -100% neutral while throttle is 0% neutral. This is just the way it is but it works perfectly and uses the whole movement for the axis.
Try these settings.
