Hi PaQ - a couple of little things - the red profile is a bit wavy instead of flat:



And also the rails although smooth to one another have a bit of an angle to their end:



Both of those things will probably cause just enough perturbations to make things a bit messy near the tip where everything collapses down together.

In the attached 3DM file, I flattened both those things out by using "flat" snap on the edit frame from a side view, and it seems to help out quite a bit.

Another thing that can sometimes help for cases like this is to put in a small circle curve as an additional profile near the tip, that kind of helps to even the shape out before it all collapses down together.

The main other tool for doing something like this would be Network, for that you'd basically mirror the scaling rail over to the other side as well and use the whole thing as input into Network - again there a small circle near the tip can help as well.

- Michael