While Ive gotten it to work well, I have a couple of suggestions, concerns, and/or questions.
I assume that radius is how big the "Tube" is, and I have no idea if angle works or that setting it to 90 just makes everything straight-ish.

On that note, is there/which setting compacts that down from a 100+ block long vein to maybe half that?
Like, in the image that whole vein, cut in half.

Can you post the .json for the example image of the curve? It isnt included in the default examples.

Finally, does Vertical and Horizontal even do anything for this vein type?

Radius is the radius of cylindrical portion of the vein. i.e. how big a cross section it is.
Angle represents how much the vein is allowed to curve. (I think.) So a value of 0 will restrict the vein to a horizontal plane, whereas 90 should allow it to be more 3D.
Horizontal and vertical size represent a "bounding box" around how big the vein is allowed to spawn - which is quite similar to how they work for other veins as well. So to cut that vein in half you would probably need to cut the horizontal size at least in half.

I can't post the JSON for the example picture as I don't have it.