On a recent hover test, I was surprised at how quickly the copter descended when switching to LAND mode to land.
The copter had never been above the LAND_ALT_LOW (10 meters).
It made me wonder if the copter has to either be above LAND_ALT_LOW, or to have flown above it for that altitude during the flight - for the copter to switch to LAND_SPEED when below LAND_ALT_LOW on LAND mode. (or technically, RTL too)
Tested in simulation with AC4.3 and LAND_SPEED is used below LAND_ALT_LOW - regardless of if the descent starts above or below that threshold. For example, initiating LAND mode at 5m with a LAND_ALT_LOW set to 10m began a descent at LAND_SPEED.
Regarding RTL, as I understand it, RTL has it’s own parameter for the “high speed”: descent rate of the landing phase. But once it reaches the LAND_ALT_LOW altitude for LAND mode, it then uses the slow speed descent rate, LAND_SPEED, that is defined for the LAND parameters.
So both LAND and RTL use the same parameters for the slow speed landing phase.