I mounted my suction cup mount in my mustang just below the rear view mirror in the center of the car (see my post on install for pix). I think the RVM might be slightly blocking the view of the escort to the rear of the vehicle. I understand the passport 8500 doesn't have a rear radar antenna though, so does it really matter? Won't the radar from behind just hit something in front of me and bounce back ? The only thing I can think of is possible rear LIDAR shots since it has a laser detector there on the top.
I was experimenting, because I moved the suction cup mount in my crappy work car up as far as possible, suction cups on the top tint, but the front of the passport hanging just below that line...I like it so wanted to try moving my mustang mount higher, but ended up going back to the way it was...mainly because I have the "pony" logo , it's like these rubber black dots, and the mount won't stick to it...thats at the top above the rvm...and mounting to the sides up high wasn't optimal because the windshield curves on the side, so it always ends up lopsided and unevenly mounted.
Anyways, rvm maybe slightly in front of the passport, any difference?