What's the black leading edge goo (1 metre from tips) in the first photo?
Zoom in on the Honeywell FasTrak tracking camera mounted above the radar dome and to the left of the wiper attachment in all 3 photos.
Doesn't like the refective leading edge and prefers to see a consistent surface length.
Matt black paint is applied and you are correct it may not have dried completely.
Apparently -
It views each blade from each rotor through a ten degree window and operates on the principle that a high-flying blade will remain in the field of view longer than a low flying blade.
It is basically a laser tachometer but analyses more info than just the RPM which will actually comes from a reference pickup on the swashplate.