At intensities that would injure, you light up the whole neighbourhood with scattered radiation. There's no hiding this attack from a sensor in the vicinity.
The math would be interesting to see. I haven't seen a directed energy antenna, but you can easily drop 9db with single digit degrees off target with a big dish.
9dB is really not a lot. If you're going to be sending 10kW+ of radiation 9dB of directionality still means you're gonna light up the whole neighborhood.
In the most literal sense of the word. 1 KW at 100 meters on a directional antenna like that will happily light up neon tubes. The field is going to be a few hundred V/meter.
