Ok, So here is another test:
Black ABS - Matterhackers - Benchy Test
Calibrated Steps/mm 441
M591 D0
Duet3D laser filament monitor on endstop input 3, disabled, allowed movement 40% to 120%, check every 3.0mm, current position -9.6, brightness 94, shutter 17, measured minimum 94%, average 100%, maximum 105% over 3972.5mm
I am using the fully enclosed mount provided in the documentation and it is mounted about 3" above the extruder. I am using a bondtech BMG extruder direct drive.
I am going to run the test again now with white ABS.