1) Laser Interceptor Version 8 (8.02 CPU and 8.8 heads). At first I bought a dual for front only, but then I ordered the 2 for the rear heads.
2) Never hit from behind that I am aware of. It's a tactic used a lot in CA, but spreading to other states. The police will sit on an on-ramp to the highway and shoot the rear of cars passing by. They will also shoot the rear of cars from an overpass and have a chase car on an on-ramp. The Escort ZR4 system has one rear head, other manufacturers have 2 rear heads and do not recommend a single rear head. The escort ZR4 is known to be a weaker jammer in real life testing results.
3) The laser emitting diode (Laser Interceptior uses a Diode) has a spread that is based on being level and parralel to the road. The manuafacturer states a horizontal install is the best way to mount the sensors.
From the USA distributor - "The Laser Diode in the LI has a shape to the beam, rectangular and horizontal, from left to right so it is best to keep the shape as designed to cover the roadway down range at the LIDAR source."
By mounting vertical you are losing coverage to shoot laser back at the laser gun and disrupt the guns ability to display a speed.
If you buy the LI Hi power version (much more expensive) there is a second transmitting diode in the sensor head, and it goes vertically. The High power heads would be better for mounting vertically because they shoot out a rectangular shape both horizontally and vertically.
If you mount heads at weird angles the path of the laser being emitted is changed and your results will be worse according to people who own the guns and have done extensive testing.
The Laser Interceptor User Manual can be downloaded here: http://www.laser-interceptorusa.com/...ser-Manual.pdf