I believe that part of the reason for an absence of markers on the battlefields may be due, in part, to the fact that there were many units, both Confederate and Union, converging on this, the I Corps' "last stand;" although, you are correct, Perrin made the most, and strongest, assault. Although I have never been to the area in which you are referring, I DO know of the chaotic situation there, as you are no doubt aware. Elements of Archer, Pettigrew, and Brokenboroughs' brigades were just emerging from McPherson's woods after driving the remnants of the Iron Brigade and Stone's and Rowley's brigades out of it. It may be possible, that although Perrin's attack was significant and terribly horrific, that, as pointed out by someone else I believe, the National Park Service simply can't cover it all, and with so many units in such close proximity, it was probably difficult to tell where Perrin, Archer, Pttigrew, and Brokenborough were during this time, etc, etc.