What the sun is doing to the asphalt
Asphalt is a mix of bitumen and filler, and the bitumen carries the oils that keep the material flexible. UV attacks those oils at the surface, and the loss works inwards year by year.
The visible result is a roof that looks dry, dull and lighter in colour than it was. The functional result is a shingle that no longer sheds water the way it did.
Heat is the second half
Roof surfaces get very hot in the afternoon and cool overnight, so the material expands and contracts daily. A shingle with its oils still in it flexes with that movement; a dry one cracks instead.
That is why a hot climate with strong sun wears a roof differently from a mild one, and why the site treats sun and heat as one exposure rather than two.
What the UV shield does
Fortify is a nanoparticle UV shield applied in one coat, and Fortify Elite is the same technology applied twice. Their role in the range is to slow the sun’s breakdown of the shingle, which is the mechanism behind the whole wear pattern.
They do not reverse damage that has already happened, and they are not a coating: the treatment works into the shingle rather than sitting on it as a film.
Why the score still decides
A roof that has already lost most of its surface is past the point where a UV shield is the answer, however strong the sun is where you live. The band decides whether the roof takes a shield, a restoration, or a bridge.
That is the difference between treating exposure and treating a roof.
What you can do either way
Watch the slopes that face the sun first: they fade and lose granules ahead of the shaded ones. If they are ahead of the rest of the roof, the roof is drying, and the score will say how far.
Shade from trees helps in theory and brings its own problems in practice, because the moisture and the growth that come with shade are harder on a roof than sun alone.