Well you won't actually find the answer without looking at the pdt (and it will be quickly obvious if there is an issue there -as it will stick out like a sore thumb.).
I do remember seeing one of those with regards to arty -and based upon what John is saying -it should have the same issue in Antietam.
So Blake- scenario name ... and artillery type please (no need for an exact unit)
Any artillery when deployed in depth and from a higher elevation will blow the crap out of massed units -particularly at close range - I have never found there to be a significant difference apart from in some scenarios the South has significantly less arty ammo (and they have to conserve their shots), whereas the Union artillery effectively has no ammo limitation in many scenarios.
In the Overland test I played Mr Nelms in one of the North Anna scenarios (the larger one) as my actual training to join the club. He was the ANV I was the AoP -and I beat him with nothing but artillery (and even at that only part of my artillery - the rifles) -by putting them on the high ground at the top left of the map where the river bends -he advanced up there -deciding to stuff me back up my own ( insert noun here) -and he managed to get caught in a cross fire and put in a position where in order to win, he had to cross the river to attack me (who out numbered him and had the river crossings covered with some Union heavy metal.). He wasn't game --- not exactly the opportunity that Bobby Lee was hoping to spring -and Mr Nelms is I think at the top of our ladder in blue.
I wrote him up some aar regarding that- and unfortunately I managed to lose that file -will have to see if he still has it.
But yeah - CSA artillery is not more potent than USA artillery, although arty might be over-valued in terms of vps -as some battles can be decided by nothing more than an artillery duel.