[wantsanagent]

"Gathering more light" is generally proportional to its planar surface. In the case of a surface film the potential increase in projected planar area is minuscule.

If you imagine an incident ray, to have a material "gather more light", that ray needs to intersect the material whereas without that material it would miss the surface. By adding some amount of height the film may cause some rays to intersect the surface that wouldn't have (primarily around the edges) but that's going to be very very small.

In general its a safe assumption that any material of the same projected planar area you put in front of another material will reduce the total transmisivity of the system.