Hello,
I’m by no means an expert, but I faced the same problem with my hardware (Cobra Defender M5 3rd gen + gametrix ECS): in each case the throttle is correctly detected in Windows, but inverted in BMS.
However I found a way to revert it by creating and configuring a virtual joystick using : vJoy 2.1.6 (virtual joystick) + UJR (universal joystick remapper)