All the Texas people are scoring pretty high on Dixie!
As a definite geographic location within the United States, "Dixie" is usually defined as the 11 Southern states that seceded to form the Confederate States of America. They are (in order of secession): South Carolina, Mississippi, Florida, Alabama, Georgia, Louisiana, Texas, Virginia, Arkansas, North Carolina, and Tennessee. This definition is strongly correlated with history and, in the minds of many Southerners, remains the traditional and emotional South.
In other ways however, the "location" and boundaries of Dixie have become, over time, more limited, vernacular, and/or mercurial. In popular mindset today, it is most often associated with those parts of the Southern United States where Old South traditions and legacies of the Confederacy live most strongly, and are most widely celebrated and remembered.
In this particular contemporary realm, there are no hard and fast lines. Roughly however, it might be an area which begins in southern Virginia (and perhaps the southern parts of West Virginia), then extends south into North Central Florida. On the northern boundary it sweeps west to take in Tennessee and southern parts of Kentucky, then continues through most of Arkansas, possibly taking in a small part of southern Missouri. On the southern end it would run through the Gulf states until the northern and southern boundary lines connect to include East Texas.
I think it has something to do with the Mason/Dixon line too. 
Geographers note that the cultural area known as "Dixie" does include the areas which you noted: a boundary line running through central VA, up into the most of KY even into far the southern 1/8th of IN, down into the southern quarter of MO, the eastern half of AR and eastern third of TX. (in TX we know that the West begins in Ft Worth and the South peters out in Dallas
) following the Gulf coastal line it swings thru central FL but excludes most of the peninsula. Geographers use several clues as to where Dixie ends and begins, some of the clues are as mundane as what is the largest Protestant denomination in towns in question. Dixie towns will tend to have Southern Baptist denoms as key churches. Although this is not exclusive. Key communities that would be markers as to location of the the
boundaries of cultural Dixie would then be : Richmond VA, Charleston WV, Cincinnati OH, St Louis MO, Springfield MO, Little Rock AR, Dallas TX, Austin TX, Houston TX, and Jacksonville FL. If one draws a line using those cities as boundary points and encloses the area inside, one gets a idea, although inexact and subject to much dispute among Geographers, as to where is the land of Dixie. The boundaries of Dixie have changed much due to in migration from the north and west during the 1960's thru to today. And one is much more likely to get the "flavor" of Dixie in the small towns rather than the larger cities of the area.
The accent itself is not confined to the boundaries of "Dixie" which as you noted is not contiguous with the boundaries of the Confederate States of America. Neither is the "Dixie" accent dominant in every area or city inside the enclosure I suggested above. The roots of much of the mountain and southwestern accents come from the South, southerners were some of the earliest settlers in much of the area. So the Dixie accent can be heard in modified form in the mountain west. I have suggested on another thread that the accents that we heard in Brokeback Mountain from characters who were native Wyomingites (Twist, Delmar, Aguirre) was in fact a bit over the top, and was actually a Texas accent. The Texans in the movie (Newsomes, Malones) however were played to the hilt and the accent was I felt right on the money.
Alternatively, the "Dixie" accent can be hard to come by in some communities that are technically a part of Dixie: Austin TX is great example of an area where the traditional Texas twang has been massively diluted due to migrations from the north and west.
Glad you added this thread, accents have always fascinated me, and I travel a good bit and love to hear legit regional accents. I fear that many of the regional accents in North American are slowly disappearing.
