Since you're mapping to a flightstick that is probably spring-loaded to return to center, you might want to map MAME's "P1 Pedal 1 Analog" (thrust) input to "Joy 1 Y Axis
-" as DarthMarino demonstrates from 1:30 - 2:05 in this video.
"Joy 1 Y Axis"
- Stick centered = 50% thrust.
"Joy 1 Y Axis
-"
- Stick centered = 0% thrust.
- Stick full forward = 100% thrust.
As always when dealing with actual analog controls, set the "INC" and "DEC" inputs to "none".
Scott