There are three elevations of note on the Cowpens battlefield, designated by the numbers 1-3.
Captain Samuel Hammond of South Carolina described the battlefield in these terms: “The ground on which the troops were placed, was a small ridge [Elevation #1], crossing the road at nearly right angles. A similar ridge [Elevation #2], nearly parallel with this, lay between three hundred and five hundred yards in his rear. The valley between was made by a gentle slope; it was, of course, brought within range of the eye; passing from one to the other ridge, the land was thickly covered with red oak and hickory with little if any underbrush. The valleys extending to the right of the general's camp, terminated in a small glade or savanna."
Hammond also stated that "The front line" was placed on "the rising ground beyond the valley," meaning Elevation #1. He noted that the second, or main line, was to be 150 yards behind the front line. Other sources either agreed with him or gave a slightly longer distance (2oo yards). This indicates that the main and militia lines were situated roughly in the positions shown below. (The contour lines are at 20-foot intervals; with access to a more fine-grain map I would perhaps shift the units slightly in one direction or another).
1 = Continental Light Dragoons, 2 = Mounted Militia, 3 = Right Wing of the Main Line, 4 = Continental Infantry, 5 = Left Wing of the Main Line, 6 = Right Wing of the Militia Line, 7 = Left Wing of the Militia Line, 8 = Skirmishers
The position of the main line seems somewhat odd being positioned between Elevations 1 and 2, rather than on either one. However, participant accounts do indicate that the main line was in this area. The son of North Carolina militiaman Thomas Lackey learned from his father "That at the Battle of the Cowpens the regulars were situated rather behind a hill" (i.e., Elevation #1). Thomas Young of South Carolina remembered that “The battle field was almost a plain with a ravine on both hands, and very little under growth in front or near us." Young was serving with the mounted militia (Unit #2 on the map above). He noted that the main line's "right flank [was] resting upon the head of the ravine on the right... [and the] left flank [was]resting near the head of the ravine on the left." The location of these "ravines" is indicated, in part, by the two creeks on either side of the main line.
Sources:John Moncure's The Cowpens Staff Ride and Battlefield Tour webpage has a transcription of the statements by Samuel Hammond and Thomas Young.
Joseph Johnson's 1851 Traditions and Reminiscences Chiefly of the American Revolution in the South is the original source of Hammond's statement.
Will Graves transcribed the pension application of Thomas Lackey (.pdf file).