Viniard Field would be the right flank of the Union army on the battlefield. There were units that stretched down to Crawfish Springs and Lee & Gordon's Mill but the right flank of the concentrated army was in Viniard Field on September 19. On the 20th it was across the road closer to the modern Wilder Tower. The important LaFayette Road runs just behind this Union line. In the second photo you can barely see a car on a park tour road on the right side of the picture (click on the picture to bring up a larger version and you can see it then). That car has just turned off the LaFayette Road. The LaFayette Road enters the treeline somewhere behind the tall monument in the second picture.
Although Bragg's plan was to drive south along the LaFayette Road and crumple this position by turning its left flank if he had got a good penetration at Viniard Field he could have altered his plan and driven north along the road. At the very least he would have found himself between significant portions of the army and been able to cause all sorts of havoc.