Hi & Welcome to the Forum.
Mounting the RD low as you mention wouldn't be a problem. Radar signal can travel underneath a vehicle between the gap & road surface. Mounting it in the grill puts it at the same physical location of the car body (or Truck body) of the vehicle ahead of you, this causes blockage of the radar EMF wave from reaching the RD horn antenna.
Stealth installs can be found here on the Forum if you're curious about doing so for both Radar & Lidar defense.

What was your username from back then if you were on RD.net ?