The goal of UV protectant (in this case) is to protect the covering material, not whatever's on the other side. On a window you are protecting the stuff on the inside of the window (furnishings, carpet, etc.). The Polyfiber method is simply used for a layman (home builder) to discern if you have enough coverage for their method (and is likely overkill). I'm suspecting the Oratex pre-impregnated material is more efficient (being factory applied) and (I believe) it has been tested to ensure it's adequate for it's intended purpose.

Greg