MH distance from water surface?

[Static]

I wouldn't say air inhibits light, but from further away the same light is spread over more surface area

[Samw]

Yup, from Table 4 in the 2nd link that I posted, the light loss of a 1x1 area when the light was moved from 6" to 12" was 43%-54% depending on the reflector used.

From Table 3 in the 1st link that I posted, the light loss of a 1x1 area when the light was moved from 6" to 12" was 36%-59% based on the reflector used.