Stealth SVX?

In CT we don't have to have a front license plate, so I took the plate and plate holder off the car. Anyway, approaching a "YOUR SPEED IS: XX" radar set up, the car before me got a quick and clear reading, but when I went by the numbers went haywire, then posted a value when I was almost on top of the sign. Given the small drag coefficient, and without the flat plate on the front, does radar have a hard time with an approaching SVX?