'double half bake' is a silly way of saying dont just bake with half the geometry. mirror your half and merge the verts along the seam before you bake instead of afterwards, and move the uvs of the mirrored part out of the normal 0-1 range (out of the square)
Something else(might be the cause, but can also pile up with what has already been told): I notice that your cage is just on one side of the object. That means that if you imagine another cage symetrical to the one you already have, you'll 'see' rays being shot in two different directions where the cages 'meet' - hence, a…
Thank you very much now I understand. I tried generating the normal map quickly in 3ds max and while still not perfect, it looks A LOT better now moving that 2nd half out of that 0-1 space. I'm going to give xNormal a try now because it seems to generate a darker shade of blue along the edges in the tangent space normal…