"Set start spline tangent" and "Set End Tangent" node for mesh spline doesn't work how i thought it would

Hey everybody! I’m trying to build some procedural-generated power lines using the construction script and a single spline.
Inside of this BP I’m constructing a bunch of smaller mesh splines between each power line-support mesh (each of THOSE are generated along my non-mesh spline using the construction script), with individual power lines connecting to each socket.
I’m trying to make the power lines sag to add a bit of realism, but every method I’ve tried for setting the tangent doesn’t seem to be working. The lines just stay taught, or disappear altogether. (if I set the tangents to x0 y0 z0 ) manually setting the tangents seems to act the way that the “set end scale” or “set start scale” should work!

Here’s some screenshots of my code:

Power-line support structure generation:


Power-line wire generation:

The latter code is less well-commented because I haven’t finalized the method.

Anybody got any ideas on why tangents aren’t working the way they’re supposed to? Anybody else having that problem?