I was designing a fiber coupler similar to https://support.zemax.com/hc/en-us/articles/1500005576542-Single-mode-fiber-coupling-in-OpticStudio.  At the very end the example in the link asks to use a coating in the coating file called ‘HEAR1’ to help with losses from Fresnel reflections. I tried to find out in the manual as to how the Zemax calculates the effects of putting such a coating but I was not able to find an answer to that. Does it use pre defined values for compensation of the reflections or does it actually calculate it by light Propagation at the air-coating and coating-lens interface.