It is the electronics in each tank that determines if theya re set at light, medium, or heavy, and also how they each respond when taking hits. light= 3 hits, med= 6 hits, heavy= 9 hits.
The tank firing makes no difference to the tank being shot. It only determines the simulated amount of armor a tank has. As for range or width of the IR, if any tanks are in the path of the beam, they will take hits. Many tankers use a shot called a fan shot. This is highly debated a it is not realistic at all and makes many unhappy during battles. What they do is fire and at the same time sweep their tank in a half moon pattern using the tracks to accomplish the maneuver.The IR is on for 1 second, so in the time period, hat tank will strike hits on anything in that path.It is very unrealistic to se and many tankers are against it.