It's certainly true that most Appalachian counties had few slaves and weren't for secession. And it's true that planter-dominated South Carolina drove the secession movement early on.
I was going more by the vote in the 1860 election. Delta counties in northwest Mississippi had very high black and slave populations, but went with the moderate Constitutional Union candidate, John Bell, rather than the secessionists' favored candidate, Breckenridge.
I took that as an indication that secessionist sentiment was also weak there, but it may have just been a political thing, since those counties were a Whig area. Maybe the big planters were all too willing to go from backing the moderate unionist candidate to supporting secession.
I notice that Davis, the other MS senator and one of the state's wartime governors came from outside of the Delta, but the other was from the area, and that nearby East Tennessee was heavily for secession. So I guess this is all something to rethink.
Eastern Tennessee was heavily Unionist, persecuted by Confederates and protected by Union troops.
Like Western Virginians, East Tennesseans considered secession from their state, but did not accomplish it.
Might that be what you meant?