Using Plate 64-3 from the OR Atlas, overlayed on a properly scaled section of the Michler map, we can find Waud's location on the battlefield.
Each side of the red square is 1 mile in length. The cyan rectangle measure 1/4 by 1 mile.
The upper left corner of the red square marks the approximate location of the "Petersburg church spires" while the cyan circle is the mine explosion.
Mortar emplacements and perspectives to the mine plume and the church spires show the very likely place where Waud saw Warren and Duane together -- the orange circle about 1/2 mile from Fort Davis.
Using Plate 64-3 we can also place the sketch-artist Andrew McCallum with Roemer's 34th NY Battery. But was this on July 30? or a month earlier on June 30?