I will try to be as clear as I can on this question.
Artillery Bounce through (Bombardment)
If I have three units all with level frontage to each other, with the centre unit being fired on from its direct front by two bases (one battery of Artillery) during Bombardment.
The rule states, the template for bounce through is placed at the back of the front rank of the targeted unit. This template width is based on the width of the Battery at is firing. This results in the template covering all of the target unit, but also the two units on each flank (in base contact)
The rule states ; Any formed unit or artillery unit within this zone [Bouncethrough zone "template"] is subject to Bouncethrough fire, regardless whether the target sustains any hits from this bombardment fire or not.
But also states; 3) Count the number of formed castings BEHIND the target UNIT that are in the bouncethrough zone.
Behind the Unit, not behind the front rank, so these two wordings appear to indicate that the flanking units are both valid and invalid targets for bouncethrough.