The rear glass on Model 3's require an extensive amounts of shrinking/molding the film to the shape of the rear glass. In order to effectively do this, the installer must have an extra amount of film to work with & pull from. The BEST most accurate way to achieve the best result is to lay more film than is needed, shrink film to glass, & then cut/trim film AFTER it's been shrunk. Rear glass piece will come in a 5'x5' sheet for the installer to shrink, trim, & install properly.
The pre-cut patterns provided are cut just slightly larger than the glass on the 4 doors. The purpose for this is to allow the installer to perform a "shave" technique on the glass for a micro-edge finish. If this is not desired, simply trim off any excess piece to desired length BEFORE installing the film.