ArduPlane Flare Height Cmd During AutoLand

[jknight100]

Bug report

Issue details
Height demand term is erroneous in flare, when using rangefinder.

Please describe the problem
Using a mature simulation with ArduPilot in the loop, and injecting radar altimeter readings from synthesized terrain.
During flight, terrain height was injected at 30ft (~10m). During autoland, altitude update occurred as expended. When flare occurs (triggered by 3 seconds to touchdown) TECS target altitude "h_dem" shows 30ft drop followed by 30ft ramp downward. Not sure why the offset is needed, and further, the rampdown seems to be in the wrong direction, causes a pitchdown cmd, and does not agree with altitude rate cmd.
Ultimately, the TECS control law minimizes error between "h_dem" and "height", so these should be in the same altitude frame. This appears to not be the case.
SEE PICTURE for simulation output.

Version
Plane-4.4.4

Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[X] Plane
[ ] Rover
[ ] Submarine

Airframe type
simulated airplane, powered fixedwing.

Hardware type
Simulated CubeOrange

Logs
cannot provide due to sensitive information

Suggested fix is to simply remove code in AP_TECS.cpp:
REMOVE: // fade across to the ideal height profile
REMOVE: _hgt_dem = _flare_hgt_dem_adj * (1.0f - p) + _flare_hgt_dem_ideal * p;
REMOVE: // correct for offset between height above ground and height above datum used by control loops
REMOVE: _hgt_dem += (_hgt_afe - _height);
ADD THIS LINE: _hgt_dem += _DT * _hgt_rate_dem;
When I make this change, flare altitude and alt cmd were nice and smooth, and agreed with altitude rate terms as expected.