The Deathwatch frag cannon has a profile that is 24" S7 AP3 Assault 2 Impact, with Impact being a special rule defined right below it as
If the target unit is within 12", this weapon's Strength is increased to 9 and its AP is increased to 2.
I played a game yesterday where I had a unit of 4 frag cannons firing at a soul grinder. 3 of the frag cannon models were within 12" and the 4th was about 13" away. How would this resolve? Would all 4 fire at S9 AP2, would I need to fire 3 of them separately from the 4th (even though it's not using a different shooting profile because it's a special rule)?
I haven't seen another rule like this, but is there a precedent, or is there maybe something I'm missing in the
BRB that outlines a situation like this? I ended up playing it the second way above, giving the benefit of the doubt to my opponent because I wasn't sure and couldn't off the top of my head think of anything that might prove it wrong other than it not being different shooting profiles, and that might not even prove it wrong as far as I know, it just seemed strange. Did I play it correctly?