Unfortunately there is no way to solve the overlapping issues, even scaling the segments (that RailClone does), because at certain point the edges of the faces intersect between them.
In this case the key is to prevent that segments overlap. This may help:
1) If the spline has corners at both directions, set the Segment Y Alignment to "Center".
2) Increase the corner radius.
3) Use higher values for Style->Geometry->Curve Steps (>100). This will create smoother corners.
4) A tip: instead creating the rounded corners in the spline, draw straight corners and use Generator->Rules->Fillet Radius, to adjust the corner radius dinamically.
Alternatively, if none of these tricks work, you would create a custom piece for the corner, and use it in the Generator (as Corner Segment). Also would be possible to define separated segments fot the inner and outer corners, using a Conditional operator (Vertex->Angle->Greater > 180).