I just noticed that the formatting of my above illustration didn't work out at all. I'll try again.
A..................................2
A..................................2 All As have range to 1, and B has range to all 2s. So all As can shoot, and all 2s can be hit.
A..................................2 It doesn't depend on whether As have range to 2.
A...........B.....1..............2
A..................................2
A..................................2
A..................................2
Possibly nobody cares.
But just in case people don't think it worked that way (that units could fire past their range as above), here's where I get it:
Under ADD UP FIREPOWER:
"Measure the range from units in the firing detachment to the target detachment using the range ruler. Add up the Firepower values of attacking units that ave a line of fire and are within range of at least one target."'
and
Under ALLOCATE HITS
" Hits may only be allocated against units that are in range and in the line of fire of at least one unit from the attacking detachment (you can't be hit if you can't be short at!)."
I suppose that in addition to what I illustrate above, you might have B and 1 near a corner, with As and 2s outside of LOS of each other, but As able to see 1 and B able to see 2s.
andy