install help

[RedRocket]

Do the three sensors need to be flush with the front of the grille inserts or flush with the grill trim to be most effective?

Flush w/ the grill inserts (meaning flush w/ the front edge of the lattice work) will perform just fine. Just try to keep the "bubble" centered horizontally, (like as shown in the pix you posted). This is b/c you want to minimize any chances of "shading" being caused if the receiving "bubble" is to close to either side of the outer chrome trim that surrounds the inner lattice work. Shading occurs when you get within a few hundred feet of the Shooter & the incoming incident angles increase dramatically the closer you get to a Shooter on either side of road shoulders.