I think the best solution is to think of the South as three areas - Appalachian South, Deep (or Gulf) South and Atlantic South. Then VA is easily in the Atlantic South since that matches the largest part of its population. NC and maybe SC is in that region, too. GA, AL, MS, and LA are the deep South. AR, TN, KY, and WV would fall in the Appalachian South by that measure. Of course its easier to make the split at the county level, but that's the issue with many states - their counties span more than one region.
That makes more sense, although I would say the Atlantic South would encompass the old former southern colonies before the expansion over the Appalachians (itself being its own sub-region: Tennessee, Kentucky, West Virginia), with the Deep South covering the territory won after the War of 1812 (plus Florida after the Seminole wars). Texas, Oklahoma, Arkansas, and certain parts of Missouri would be another sub-region I would probably call the Frontier South.
