(Doug, Margot, Jeff)
We setup the Newport laser collimator and retro-reflected the beam from the First Contact thin film coated HR surface and measured the power both in front of the optic and measured the transmitted power through the optics (2 optics and 2 separate measurements) with and without the First contact. Measurements were taken at ~3M and ~6M distance from laser collimator to HR side of sample optics. Sample optics were coated for 1064nm with both HR and AR coatings and First Contact sprayed on the HR surfaces.
I didn't see a need to set up a BS and try to measure a true reflect from the HR surface. The small difference would still be int the absorption and diffused beam if present and is within usable range.
Parameters:
Newport laser collimator beam dia  ~3.0 cm dia.
Ophir power meter aperture 1.2 cm ²

optic s/n 11: @ 3.0 meters
power at 0º incidence in front of optic 44.4µW
power transmitted through First Contact 39.4 µW = 85.6% T
power transmitted through without First Contact 38.0 µW = 88.7 % T (higher reflectivity)

optic s/n 38: @ 3.0 meters and 6.0meters
power at 0º incidence in front of optic 42.4µW
power transmitted through First Contact 36.5 µW (3.0 meters) = 85.6 % T
power transmitted through First Contact 36.4 µW (6.0 meters) = 85.6 % T
power transmitted without First Contact 34.2 µW (6.0 meters) = 80.7 % T (4.9 % higher reflectivity)

No retro-reflections interference noticed.

"This may work"
Doug