My PPF installer recommends against installing both exterior WPF and interior windshield tint. Each film has a different refraction index which in turn differs from the glass index, with the laminated windshield itself already having a film between the two layers of glass. Each layer brings an added risk of refractive distortion. This risk increases with the slope of the windshield, and the Gravity windshield is raked fairly steeply.
I opted to use only WPF, as the factory windshield blocks almost all UV light, anyway, and the new tint technology on the upper canopy has pretty good IR rejection, too.
The Xpel WPF I used was 40" wide. I was going to have them put a second width over the rest of the front canopy section (back to the B pillar), but when I saw how invisible the line was I didn't bother with the rest of the front canopy, as it is at much lower risk of an abrasive hit. And the line lands right across the middle of the visor line, so you don't notice it from either inside or outside the car. In fact, when I'm cleaning the windshield I sometimes have to feel for the line with my fingers, as I can't always see it even when I'm looking.
Also, notice that the WPF only has a 12-month warranty vs the 10- or 12-year warranty of the PPF. That is because the WPF has a much shorter service life and will likely have to be replaced several times during the life of the car. Stopping at the visor line will reduce the cost of replacement.
