Not trying to be nit-picky here, but the position of Hovey's cannons is key to understanding the flow of the battle and helps explain the position of Boomer's men and Holmes' and Hovey's men at the Confederate high tide. The Confederates did not push the federal troops off Champion Hill, but were stopped on top of Champion Hill, with Holmes and Hovey astride the Jackson Road in an unassailable position and Boomer holding his own on the refused flank of Logan's Division. Timothy Smith makes the point that the Confederates could see the federal wagon trains, but that's not unlike me saying I can "see Louisiana" from Fort Hill. Hovey's batteries in the former situation, like the Mississippi River in the latter situation, made that opportunity an impossibility.
Interestingly enough, Cadwallader claims Grant himself placed the batteries, which would mean that he understood just how strong Holmes' position was and knew that the only possible direction the Confederates could reasonably go was east between Holmes and Boomer. Amazing that he could have such a perfect grasp of the operational situation amid all of the chaos.
Should be an interesting day of events. I look forward to attending if I can make it.