When looking at the explanation here:
"Whether you need to pull back on the elevator stick or push forward to climb depends on the setting of the
FBWB_ELEV_REV parameter. The default is for pulling back on the elevator to cause the plane to climb. This corresponds to the normal response direction for a RC model. If you are more comfortable with the reverse you can set FBWB_ELEV_REV to 1 and the elevator will be reversed in FBWB mode."
But in Mission Planner, it seems to say the opposite, that the elevator DOES need reversed to behave normally. Mission planner is saying when set to 0 (which is default), the behavior of the elevator is REVERSED:
"Reverse sense of elevator in FBWB and CRUISE modes. When set to 0, up elevator (pulling back on the stick) means to lower altitude. When set to 1, up elevator means to raise altitude."
And I can attest, that when flying my quadplane in early flights, I could not understand why FBWB was making the plane DESCEND when I pulled the stick BACK. I thought I had airspeed or throttle problems, when all along I think this setting was wrong…which again, is confusing when reading the docs as compared to Mission Planner.