Rule 7.52 Separate Column Modifiers

[Coniglius]

HI guys,  playing Hopeless But Not Serious Scenario 6, and I have a question regarding bombardment fire. Here is the situation:

1. The Austrian mortars have a shot at a German artillery unit that is currently limbered and being towed by a wagon. 
2. Austrians attack at an '8' with modifiers for:
   a. target being artillery (+1)
   b. target is spotted by firing unit (+1)
   c. target is loaded wagon (+1)
3. Austrian Mortar now attacks at the '21' column... or do they? 

Here's my dilemma... is this two separate attacks (one vs the artillery at the 16 column and one versus the wagon) or does rule 5.67 apply where the attack is made against the wagon, and the effects are felt by both the wagon and the artillery? 

I know the answer is in there somewhere, but I can't find it.  Thank you in advance!!!