I don't follow.
Some quick rough math, based on the CSA military deaths estimate (950k), a 16 mil to 8 mil pre-war white-to-black population ratio (taken from
this post and
this post from KingSweden in the OG discussing the 1910 CSA Census), and my own estimate of roughly 500k excess White Confederate civilian deaths from all sources, including but not limited to: US war crimes (reprisal killings, terror shelling/bombing), collateral damage (from both sides), famine, disease, and a potential, may-or-may-not happen slave uprising.
That gives us roughly 1.5 million White Confederate deaths as a result of this war, give or take. Given 8 million pre-war Black Confederates, you'd only need roughly 10% (800k) of them to make their way to Kentucky in order to have a proportionally equal population loss (given the 2:1 ratio), and, IMO, that is a very low estimate for the number that will eventually end up there (I'd assume the number ends up being at least double that). And that's, again, before taking into account excess Black Confederate deaths, which will likely be considerable when it's all said and done.
Now, the math is complicated by the secessions of Kentucky and Texas, and the loss of the Arizona. IIRC all 3 had significantly lower enslaved populations (proportionately) than average, which will help lower the ratio in the rump Confederacy. Without knowing the exact percentages, as well as the percentage of war-related deaths that come from the seceded areas, and additionally the number of white Kentuckians who end up fleeing south of the border, its impossible to say for sure.
I think, at best, the ratio remains unchanged from pre-war. And even then that would be almost entirely due to Texas's secession; Taking all of the pre-war Confederacy's territory, excluding Kentucky (for obvious reasons) the ratio would almost certainly be higher.