Negative. Counterbattery fire is conducted as part of the bombardment phase regardless of the position of the bombardment units in question. If your Medium Bombardment is in a support position and it fires on my Medium Bombardment in a Front Line position my unit will counter fire back at it. If your LR Bombardment shoots my LR from the Rear Position and I have it in the Front Line position it will fire back.
However, the caveat is that this will only happen if that enemy bombardment element targets the formation that my bombardment element is a part of. So during the bombardment phase, if nothing targets the formations containing my Mediums, LRs or Heavies, they won't engage in counter battery fire at all. They also won't engage in normal bombardment either, so they sit idle during that phase unless their formation is shot at.
Putting them in Support or Rear formation let's them engage during bombardment. I don't remember if it affects counter-battery fire or not, I think you need to assign them to direct support to do that, but I'm not entirely sure of it. What I am sure of is that if you put Medium Bombardment or higher in a Front Line formation it can partake in counter-battery fire, but only in a very specific capacity.
Do you have any citations for this, or is this from gameplay observation? Because that is definitely not how the wiki's quotes talk about counterbattery fire working.
"Once all front line attacks have been concluded, each unit in each element providing supporting bombardment will engage either the hostile formation being targeted by the friendly formation they are supporting, or one of the hostile formation's own supporting elements (counter-battery fire). If the hostile formation is targeted, each unit in the supporting artillery element engages a random element in the hostile formation, with the randomisation based on the relative size of the hostile formation elements (the same as front-line vs front-line). If a hostile supporting element is targeted, all fire is directed against that element. This represents the difference between providing supporting fire in a combined arms front-line battle and targeting specific hostile artillery for counter-battery fire. The decision to target the hostile front-line formation vs hostile support elements is based on the relative sizes."