A good question, and this is really only applicable for short shooting units like Gnoblars, Skinks, people with Pistols, etc.
The reason the rules mention such an obscurity is to keep players from saying 'I'm going to stand and shoot, but I'm going to only fire when you're within X" so I don't suffer a long range penalty'
I'm not sure whether or not Gnoblars even suffer this penalty. Long range is equal to the second half of your shooting range (so a long bow has a range of 30", short range is 1"-15" and long range is 16"-30")
So as the enemy charges, if you have Gnoblars that would be in range with their missile attack (throwing trash, which I think has an 8" range) then they can fire.
Keep in mind that the only models that get to make a stand and shoot reaction are ones who can see the charging unit. So in your example, it might not be possible for each guy (esspecially the ones on the end of the formation) to get to stand and shoot.
Also, I'm pretty sure that you can shoot in two ranks for a charge reaction if you are on a hill.
The reason the rules mention such an obscurity is to keep players from saying 'I'm going to stand and shoot, but I'm going to only fire when you're within X" so I don't suffer a long range penalty'
I'm not sure whether or not Gnoblars even suffer this penalty. Long range is equal to the second half of your shooting range (so a long bow has a range of 30", short range is 1"-15" and long range is 16"-30")
So as the enemy charges, if you have Gnoblars that would be in range with their missile attack (throwing trash, which I think has an 8" range) then they can fire.
Keep in mind that the only models that get to make a stand and shoot reaction are ones who can see the charging unit. So in your example, it might not be possible for each guy (esspecially the ones on the end of the formation) to get to stand and shoot.
Also, I'm pretty sure that you can shoot in two ranks for a charge reaction if you are on a hill.