Oddly, I might do it a little differently. I design the end of the tail, so the blending process will be easier, in that the whichever blend method you use won’t have to go around the shoulder end of the underside of the tail.
This is just a quick suggestion, and I don’t have your work, but I just wanted to show what I mean.
I brought a copy of the airfoil wire down, widened it, and matched where you cut, but this is no substitute for doing this upstream. The cap I made was just a quicky curve network, but it’s using a rotated extrude, which is unsuitable for blending, as are the slight concavity.
Anyway, my idea is: make the blend as much as you can on a single plane.
BTW, you know about NACA generator, correct?