I think what they are saying is that if there is a gap between the film and the actual image producing screen it may become opaque.
Kinda like a privacy shower door or something.
If the person in the shower gets real close to it people can see what's going on.
But if they step back from it then it becomes more opaque and unclear.

So they want the film applied directly to the image producing screen.
Which in your case wouldn't help the glare situation.
Wonder if there is like an automotive window "tint" of sorts that would work ?