Sight radius is 35 not 30.
Range check is for each entity separately.
In addition some time vision/shot blocker prevent a unit from firing but not from being fired upon (seen it happen more with vehicles not sure if it happen with infantry).
Some unit get extra range (pathfinders, Fall, PTRS)
Thanks for the correction although it actually doesnt change the context. Extra range could also be not the reason as the unit in question were riflemen and Panzergrenadiers. So it leaves the explanation with shot blocker. That is indeed a good point. However, the field between mentioned units was plain grassland.