The EK2_RNG_USE_SPD with his small possible values of 2.0 - 6.0 meters per second makes no sense to me on a plane.
The range finder will not be used as the primary height source when the horizontal ground speed is greater than this value.
Almost no plane can fly at less than 6 m/s while it make sense for a copter
I guess that this parameter is not used during AUTO mode but perhaps only during plane landing.
It could be useful if someone want to fly close to ground using a range finder but the value must be increased to an higher value , lets say 20 m/s